Weather456's Tropical Weather Blog

Tropical Update; NOAA's Prediction; SAL

By: Weather456, 11:07 GMT le 31 mai 2009

Tropical Update

The weather pattern remains very much of the same across the Atlantic as 24 hrs ago. Fair weather remains across the Southeast United States due to surface high pressure supported by dry subsidence with an upper trough digging across the region. The Gulf of Mexico remains a bit less stable with mid-upper level moisture advection occurring between the upper trough over the CONUS and an upper ridge over the Eastern Pacific. This diffluent flow is helping to generate scattered showers and isolated thunderstorms over Mexico and the Gulf waters. At the leading edge of the upper trough, a frontal boundary extends from the Atlantic across Southern Florida and into the Gulf of Mexico. Scattered to numerous showers remain within 120 nmi ahead of the front over Cuba and the Bahamas.

A broad upper trough also extends across the Caribbean region helping to generate showers over Central America and northern South America along its base and generate scattered cloudiness and moisture across the Windward Islands along its eastern flank. Dry subsidence remains at the heart of trough allowing fair weather to dominate most of the Caribbean Sea.

Infrared and short-wave imagery continue to show the presence of a surface trough near 60W with a evident band of low level moisture at the leading edge of the trades. If the upper trough over the Caribbean continues to intensify, it may allow further amplification of the trough causing low level moisture to spread over the Northeast Caribbean.

The centralized subtropical ridge continues to maintain moderate trades across the tropical Atlantic with dry subsidence weather apparent in satellite images; likely due to a layer of Saharan Air Layer.

Satellite animations this morning showed some improvement in the structure of Tropical Invest 90E (Eastern Pacific) with cloud clusters organize in and around the low pressure area. The environment remains favorable for some development of this system as it tracks towards the west.



My Thoughts on NOAA Hurricane Season Outlook

On 21 May 2009, the National Oceanic and Atmospheric Administration (NOAA) issued their official outlook on the 2009 Hurricane Season, predicting 9-14 named storms, 4-7 hurricanes and 1-3 major hurricanes. Comparatively, on 16 May 2009, I forecasted 12-14 named storms, 6-7 hurricanes and 3 major hurricanes.

The conditions NOAA observed in March-April in regards to enhanced tradewind flow across the Main Development Region (MDR) due to a stronger than normal subtropical ridge was in close agreement with the forecast I presented. Both forecast explained the cool sea surface temperatures in the MDR was likely due to the fact of increase evaporational cooling by the tradewinds.

Suppressed rainfall along the Intertropical Convergence Zone (ITCZ) over the tropical Atlantic (NOAA) and Africa (Weather456) was another similarity between the two forecasts and this factor will likely not contribute to the overall numbers of the season, especially in the tropical Atlantic region of the MDR.

The most important and striking connection between the two forecasts was the mention of forecast uncertainties with this year’s hurricane season, due to number of factors stated by NOAA.

One area where the two forecasts did not agree completely was on the topic of the El Nino Southern Oscillation (ENSO). While NOAA stressed the uncertainty with ENSO this year, I gave a clear-cut prediction. Despite both forecasts mentioning the majority of models show ENSO-neutral conditions and that El Nino could develop, I failed to reflect this uncertainty in the forecast numbers. I still think neutral conditions will last into at least August but the development of El Nino is quite possible and whether its effects lag or not, define the uncertainty.

Understanding the Atlantic Hurricane Season: The Saharan Air Layer


SAL conceptual model illustrating the following properties: geographic location of the African continent, ICTZ, and dust plume, surface flow (solid yellow arrows), particle trajectories (dashed yellow arrows), mid-level easterly jet (thick red arrow), 700 hPa wave axis (thin red arrow), regions of convection, and the rise of the SAL base to the west (Karyampudi et al. 1999).

Intense heating over Africa during the Northern Hemisphere Summer creates surface low pressure (a heat low) which enhances inflow and convergence. The convergent air rises in turbulent convective currents to the 500 mb level leading to a dry, well mixed layer.

The temperature/moisture/pressure gradient between the arid Saharan Desert and the moister Guinea coast causes a general low level flow from the Gulf Guinea north into the desert. The resulting thermal wind flows at 700 mb from the desert to the Gulf but is reflected to the right of motion due to the force of Coriolis. This thermal wind becomes an easterly jet known as the African Easterly Jet (AEJ or MLEJ). Instability south of the jet causes African Easterly Waves (Tropical Waves).

During the passage of these waves, the pressure gradient fluctuates and the resulting wind shift allows dry well-mixed layer of dust to leave the African coast and travel westward in what we call the Saharan Air Layer or SAL.

What is the Saharan Air Layer?

A dry, well mixed layer of dry air that formed over Northern Africa during the summer and propagate westward across the tropical Atlantic, sometimes reaching as far as the Caribbean and United States.

How Does the Saharan Air Layer formed?

Due to intense heating over Africa which causes air to rise in turbulent convection which help suspend dust particles in the lower troposphere.

At what level is the SAL normally found?

About the surface to 500 mb.

How does the SAL layer propagate from Africa across the tropical Atlantic?

Through the pressure and wind fluxes brought out by passing tropical waves.

What are the impacts on tropical disturbances?

The entrainment of mid-level dry air suppresses convection by cooling the mid-levels and resulting in downdrafts rather than updrafts. Though there have been cases where the associated AEJ help to increase positive voricity along initial disturbances, like Tropical Storm Ernesto in 2000.

How Do I Track the SAL?

The Saharan Air Layer can be tracked by various tools. My favorites include total precipitable water (PW) loops and SAL products by the CIMSS; and visible satellite imagery. In the former, SAL is indicated by low PW values while in the latter; SAL is indicated by a hazy, milky appearance. Be sure not to confuse this milky appearance with circus clouds. Other tools include aerosol mapping, RGB imagery and MODIS imagery from NASA.

Saharan Air Layer Variability

The main variability of African dust includes November-May Rainfall over Sahel and the strength and position of the Subtropical Ridge. Drier Sahel rainfall increases the chances of dust concentration over the continent but is rather more complicated than that. Drier conditions also contribute to less intense African Tropical Waves and as we saw, these waves help propagate the dust into the Atlantic, so fewer waves could mean less dust events.

The other factor is not well understood but, the strength and position of the subtropical ridge can determine how the dust propagates westward.

Interesting Facts

The SAL sometimes contributes to spectacular sunsets due to the refraction caused by the dust particles.

The SAL reduces air quality, especially in the Lesser Antilles and evidence of the SAL is sometimes evident by the milky and hazy appearance when looking at the sky, along with the aforementioned spectacular sunsets.

The SAL is an intraseasonal modulator of not only tropical cyclone activity but the rainy season over the Caribbean.

The aerosol particles in the SAL can act as condensation nuclei for the formation clouds.

Some of this information was made possibly by Phoebe Anne Woodworth; Division of Meteorology and Physical Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida


Photo of the Saharan Air Layer taken from the NOAA P-3 Orion after SALEX mission 20060918h during the ferry back to Barbados. Saharan dust gives the sky an orange glow during this late afternoon sunset in the eastern Caribbean. Small cumulus clouds can be seen poking through the tops of the dust layer. Photo credit: Jason Dunion NOAA/HRD.

Understanding the Atlantic Hurricane Season: The SST Factor
Understanding the Atlantic Hurricane Season: Technical Terms
Tracking Tropical Cyclones Part 1: Center Fix
Tracking Tropical Waves
Understanding the Atlantic Hurricane Season: Vertical Wind Shear

My next blog will be on Monday and will discuss June climatology and June 2009 outlook.

Visitor Map
Create your own visitor map!

Updated: 11:34 GMT le 31 mai 2009

Permalink

Tropical Update; Hurricane Prepardness; 2009 Vs 2004

By: Weather456, 12:45 GMT le 30 mai 2009

Tropical Update



This morning’s visible satellite imagery shows that the remnant of Tropical Depression One is located just south of the Canadian Maritimes along a frontal boundary draped across the region. This time frame coincides with 72 hr precipitable water loops which showed the system being absorbed.

The Southeastern United States and most of the Gulf of Mexico remains high and dry due a large upper trough supported by surface high pressure. A frontal boundary draped across the Eastern Seaboard marks the leading edge the frontal system with scattered showers and possible thunderstorms within 120 nautical miles ahead of the boundary.

A similar weather pattern is over the Caribbean with surface high pressure being supported by subsidence within a broad upper trough across the region. Scattered showers and thunderstorms are found at the base of the trough over Central America, South America where diffluence is greatest, with high clouds streaming over the Windward Islands. An upper low is embedded within the trough north-northeast of Puerto Rico and will help modify the dry weather across the Northeast Caribbean and Puerto Rico.

Meanwhile, QuikSCAT and visible imagery clearly identified a surface trough over the Central Subtropical Atlantic near 55W with clear curvature within the low level cloud and wind fields.

In the tropical Atlantic, the surface Azores High is maintaining a band of 15-20 knot trades and fair weather. This weather pattern is being further enhanced by a region of Saharan Dust between 40W and 20W. A possibe tropical wave near 20W.

The first Tropical Invest of the 2009 Eastern Pacific Season was designated this morning with an area of disturbed weather associated with a tropical wave. Some gradual development of this system is expected over the next couple of days. It doesn't seem a threat to land as of now as it tracks west.

Recapping This Week’s Hurricane Preparedness Theme

1. First, get important papers and special photos in order and secured in plastic. Identification is difficult and time-consuming to replace: so be sure to include social security cards, birth certificates, high school diplomas or GED certificates, titles or deeds to property. Photos of special occasions or loved ones cannot be replaced, so including these is important as well.

2. Think ahead and take video or photos of your property before you leave. This will help later on with any insurance checklist claims for damage that may need to be filed.

3. If staying with relatives is not an option, consider booking a room in a hotel or motel in another nearby town or state. Make sure to get directions and put them in the car ahead of time. It is easy to forget that piece of paper in the rush out the door. A cheaper route might be to find temporary hurricane shelters. Usually nearby towns not in the direct path of the hurricane will provide these for people in need.

4. Unfortunately, it is unlikely that your pet will have a place in a motel or hotel. Keep this in mind and try to find alternate housing for your loved one until it is safe to return, or check out pet-friendly hotels in your area.

5. Designate a spot, in the hall closet, to keep a bag of clothes for each person in the household. Make sure to include sleeping gear if you plan on going to a temporary shelter.

6. Along with overnight clothes, consider stocking your Hurricane Kit with the following: extra cash, generator, batteries, flash lights, battery operated radio/television, bottled water, toilet paper, non-perishable foods such as cereal or crackers, canned goods, can opener, a small cooler, candles, prescription medicines and any over-the-counter remedies you use regularly; and if you have small children - diapers, baby wipes, formula, baby food.

7. Count on the power being out for at least a day or two. Remember that ATM's will be non-operating, so have at least some hard cash in your Hurricane Kit (see no. 6, above) to see you through the storm.

When TV and computer games no longer operate, board games or a deck of cards come in handy! Arts and crafts, crayons and downloadable coloring pages are always great distractions for the kids - so make sure you've stored some of these supplies in a tote bag or in the car trunk.

8. If you decide to tough out the storm, stay downwind in your home. This means if the wind is hitting the living room windows, go to the room opposite the living room.

9. Plywood is a 'hot' commodity for those of who decide to stay. Boarding up windows that will take the brunt of the wind and rain is the wisest decision. If board is not available, protect your windows from the wind by criss-crossing them with layers of duct or packing tape. This will be enough protection for light-to-medium winds, but learning how to build and install plywood hurricane shutters is your safest bet. If you can afford it, have them installed by a professional.

10. Finally, STAY INSIDE. However tempting it may be to videotape or take photos of the storm, be sure to shoot from indoors - where it's safe, and dry!

2004 Vs 2009; Similar or Different

Over the past two days I did some analysis of years, 2004 and 2009, in regards to tradewind flow, ITCZ, sea surface temperatures, ENSO, mean sea level pressure and African Rainfall. The analysis revealed 2004 may not be as different from 2009 as many think. For one example, the NAO/MSLP was about the same and trades ran 5-10 knots higher in 2004 than 2009. Another example is that the cool anomalies in sea surface temperatures we are seeing in parts of the Atlantic this year, like north of the Bahamas and Hispaniola and along the West Coast of Africa was present in 2004. The only difference is, the warm anomalies just east of the Lesser Antilles extended further north in 2004. However, at this time, the data is inconclusive, and further analysis is required. I am expected to post a blog on this topic in June.

Visitor Map
Create your own visitor map!

Updated: 21:05 GMT le 30 mai 2009

Permalink

Tropical Depression One/Brazilian Floods Continue

By: Weather456, 09:43 GMT le 29 mai 2009

Tropical Depression 1 is located near 39N-66.0W, moving off towards the east-northeast based on the latest short-wave infrared imagery. Estimated surface winds are near 30 knots with a minimum central pressure of 1007 millibars based on Dvorak shear patterns and surface observations. Satellite imagery this morning showed pulses of convection near and around the eastern semi-circle of the depression due to a bit of westerly shear affecting the system. The depression appears to possess a well-define circulation but is having trouble getting sustain convection around it. The depression still has a slight chance to become a tropical storm later this morning as it continues along the edges of the Gulf Stream and moving into a region of lower shear. However, as time progresses this becomes more unlikely as baroclinic forces will begin to take hold of the system as early as tonight and into Saturday. No land areas are expected to be affected but some ships may have to divert their tracks. This time last year, we were tracking Tropical Storm Alma as it impacted the west coast of Central America.



Elsewhere in the Tropics

Upper level troughing has entered the Caribbean region helping to generate showers along its base from the Bay of Campeche, across Central America and northern South America. An upper level circulation is embedded within the trough near Haiti and is helping sustain lingering moisture across Cuba, Hispaniola, Puerto Rico and to a lesser extent, the Northeast Caribbean.

General Outlook...The surface pressure/weather pattern remains unchanged over the next 24 hrs with an increase chance of moisture entering the Western Caribbean due to a frontal boundary. Increase chance of moisture along Central America and Hispaniola due a combination of upper diffluence and daytime heating. Otherwise, dry weather expected.

Convective Outlook...Central America south of 15N, Western Cuba, Eastern Jamaica and parts of Hispaniola

High Seas/High Wind... 7-11 ft seas and 20-25 knot winds in the central Caribbean Sea due to the pressure gradient between the Colombian Low and the subtropical ridge

Brazil Floods Continue

I covered this story about 2-3 weeks ago about the enormous amount of rainfall that is falling across Northeast Brazil since April 2009. Since then, the death toll has risen from 31 to 49 and with damages reaching 400 million dollars across 12 affected states. Nearly half of a million persons remain homeless and displaced and unable to return back home as the rains are expected to continue for another 2 weeks. Most recently, a dam broke in the city of Sao Paulo, right along the Atlantic coast killing 4 people with 11 missing. The waters swept away homes, trees and electrical energy towers and left behind muddy river beds filled with splinters and large dislodged rocks.

"It was like a tsunami with total destruction, especially in the areas close to the dam," Gov. Wellington Dias of northeastern Piaui state told reporters after touring the devastation zone.

Some experts say that wild climatic changes are the cause of these floods but weather-wise, the floods are being caused by the anomalously southern extent ITCZ due the stronger than normal subtropical ridge over the Atlantic coupled with warm sea surface temperatures and the monsoon rainy season. As the ITCZ shifts north over the upcoming weeks, these rains should subside and the dry season could commence. Places further north such as Suriname, French Guiana, Guyana, Venezuela and Trinidad, could see their rainy season by mid-June if forecast verifies. For further reading check out TRMM Brazilian Floods.





Hurricane Preparedness Tips

Continuing with this week's hurricane preparedness theme:

9. Plywood is a 'hot' commodity for those of who decide to stay. Boarding up windows that will take the brunt of the wind and rain is the wisest decision. If board is not available, protect your windows from the wind by criss-crossing them with layers of duct or packing tape. This will be enough protection for light-to-medium winds, but learning how to build and install plywood hurricane shutters is your safest bet. If you can afford it, have them installed by a professional.

10. Finally, STAY INSIDE. However tempting it may be to videotape or take photos of the storm, be sure to shoot from indoors - where it's safe, and dry!

We'll recap all tomorrow. Hurricane Season begins Monday, be prepared!

Visitor Map
Create your own visitor map!

Updated: 10:14 GMT le 29 mai 2009

Permalink

Tropical Update/New Caribbean Outlook

By: Weather456, 10:29 GMT le 28 mai 2009

A weak low pressure continues to shift towards the east-northeast, now located near 36N/74W with an estimated central pressure of 1008 millibars and winds near 25 knots in a small portion in the eastern quadrant. This morning’s satellite imagery showed that a small area of convection being generated near the center but alas, this maybe too late for 91L. Despite the storm moving under 10 knots of shear it is expected to move over waters too cold for tropical cyclogenesis. In addition, the storm is expected to either dissipate to merge into a larger frontal system by Friday as it continues off towards the northeast/north-northeast. The storm already estimated to have dumped an inch of rainfall, locally up to 2 inches across the Outer banks of North Carolina, brought gusty winds which may have produce 3-5 ft swells.

Tropical Depression One

91L managed to continue to develop persistent deep convection near its center during the morning hours and was upgraded to Tropical Depression 1 at 11 am. This marks the 3rd consecutive year that a tropical depression formed in May; it is also the first time, since 2003 that the Atlantic started earlier than the Eastern Pacific. Tropical Depression One should become a tropical storm later today as it continues to traverse the relatively warmer waters of the Gulf Stream and under 10 knot shear. No land areas will be affected as it pulls off towards the northeast but 5-6 ft swells may reach the NE Coast of the United States. This system is expected to become extratropical by Saturday.





A large area of convection in association with a pre-frontal squall line continues to propagate across the Eastern Gulf. This system is a classic squall line; characterized by an area of convection that formed along a frontal boundary across the Texas coast in the late afternoon and propagate out ahead of the front due the spilt in upper jet stream. The squall line moves and sustains itself by the regeneration of thunderstorms along downdraft boundary (outflow boundary). Squall lines are mesoscale convective systems, so are tropical cyclones and mesoscale convective complexes. They normally peak during the night and weaken by morning, but this one might be able to sustain itself until it reaches the west coast of Florida bring gusty winds and possibly flooding rains.

This is a new product that has been requested by Caribbean readers of the blog. The first section of the outlook includes a current synopsis of the region. The second line includes a general outlook for the remainder of the day. The third line includes areas of high risk of thunderstorm activity mainly in the form of tropical cyclones, afternoon heating and sea breeze convection. The fourth line includes an outlook of high wind and seas across the region and its cause.

Caribbean Outlook

Synopsis...Surface high pressure dominates most of the region along with a region of relatively dry air, providing fair weather and light to moderate trades, especially across the Eastern Caribbean. A combination of speed convergence and upper divergence ahead of an upper level feature over the SW Atlantic continues to produce lingering moisture across Hispaniola, Puerto Rico and the SW Atlantic. Additional scattered showers with isolated thunderstorms across parts of Central being generated north of an upper ridge over the eastern Pacific basin, as it interacts with the ITCZ and passing tropical wave.

General Outlook...High pressure will continue to build across the region increasing the chance of fair weather across the Lesser Antilles and parts of the Northern and Central Caribbean. There is an increase chance of convective precipitation across Cuba, Hispaniola and Central America later today due to the upper level pattern. In addition, lingering or debris moisture may spread across the Northeast Caribbean and Trinidad but otherwise dry weather expected.

Convective Outlook...Central America south of 15N, Central Cuba and Hispaniola

High Wind/Seas Outlook...7-10 ft seas and 20 knot winds in the central Caribbean Sea due to the pressure gradient between the Colombian Low and the subtropical ridge.



Hurricane Preparedness Tips

Continuing with this week's hurricane preparedness theme:

7. Count on the power being out for at least a day or two. Remember that ATM's will be non-operating, so have at least some hard cash in your Hurricane Kit (see no. 6, above) to see you through the storm.

When TV and computer games no longer operate, board games or a deck of cards come in handy! Arts and crafts, crayons and downloadable coloring pages are always great distractions for the kids - so make sure you've stored some of these supplies in a tote bag or in the car trunk.

8. If you decide to tough out the storm, stay downwind in your home. This means if the wind is hitting the living room windows, go to the room opposite the living room.

Visitor Map
Create your own visitor map!

Updated: 17:38 GMT le 28 mai 2009

Permalink

Tropical Invest 91L

By: Weather456, 10:22 GMT le 27 mai 2009

Tropical Invest 91L is centered near 34N/75W moving off towards the north with an estimated central pressure of 1009 millibars and winds of 25 knots based on surface observations and an ASCAT pass from 0100 UTC today. This morning’s satellite imagery showed a defined low level center but with little associated convection, producing scattered showers along the Outer banks of North Carolina. The little convective activity is likely due to the comparatively cooler waters on the eastern edge of the Gulf Stream which is unable to sustain deep convection. This system still has the potential to organize today as it moves over the warmer part of the Gulf Stream, coupled with 5-10 knot wind shear and ample moisture. Regardless of development, expect this system to continue off towards the north, passing close to the coast of North Carolina later today, exiting off towards the northeast by tonight and on Thursday; and absorbed into a larger system by Friday. Less than 1 inch of rain is expected along the coast due to 1) the lack of deep convection and 2) the asymmetry of convection on the east. The storm will produce up to 10 ft seas over open waters with 3-5 ft swells reaching the coast. I will continue to monitor the system.

IR Satellite Animation



Nexrad Radar



Offshore Reports



Hurricane Preparedness Tips

Continuing with this week's hurricane preparedness theme:

5. Designate a spot, in the hall closet, to keep a bag of clothes for each person in the household. Make sure to include sleeping gear if you plan on going to a temporary shelter.

6. Along with overnight clothes, consider stocking your Hurricane Kit with the following: extra cash, generator, batteries, flash lights, battery operated radio/television, bottled water, toilet paper, non-perishable foods such as cereal or crackers, canned goods, can opener, a small cooler, candles, prescription medicines and any over-the-counter remedies you use regularly; and if you have small children - diapers, baby wipes, formula, baby food.

Visitor Map
Create your own visitor map!

Updated: 10:37 GMT le 27 mai 2009

Permalink

Tropical Update

By: Weather456, 10:29 GMT le 26 mai 2009

An area of disturbed weather, in association with a surface trough of low pressure, continues to produce disorganize showers over parts of the Central-Southern Bahamas, the SW North Atlantic and up along the US East Coast. Shortwave infrared and water vapor satellite imageries this morning showed convection has waned as compared to yesterday with mid-low level cyclonic turning evident near 27N-75W. Surface observations indicated an area of low pressure forming in the vicinity but as to whether it possesses closed winds is uncertain. Some of the global models agree on developing a weak low pressure from this disturbance and move it towards the north and slightly east thereof under the influence of a building ridge across the Southwest Atlantic. Along this trajectory, it should skirt or pass over North Carolina in about 48 hrs and then turn out to sea. The timing of the high in relation to this system will determine either situation. Intensity of this system remains uncertain. Vertical shear is decreasing north of the system and is expected to continue to do so. Sea surface temperatures are relatively warm due to the Gulf Stream and the system is expected to be of a shallow warm-core type. However, the system is forecast to begin to interact with an advancing frontal system currently over the Northern Great Plains in about 60-72 hrs. Eventually the whole system will become absorbed by 80 hrs offshore the Northeast United States. The area will be monitored until then. Regardless of development, moisture is expected to spread along coastal South & North Carolina. At its closest approach, 3 ft surf may affect anywhere from South Carolina to New Jersey.



Atmospheric Blocking

Over the past 2-3 weeks, the atmospheric blocking across the Eastern Atlantic has been relatively strong. This has lead to a persistent weather pattern to linger over the Northern Caribbean, Bahamas and Southeast United States. It is responsible for the long-live non tropical low that spun for days near Bermuda, the genesis of 90L from a secluded frontal trough and now reemergence of moisture near the Bahamas. There is little west to east motion resulting in a lingering weather pattern. This should change as the blocking strength subsides.

Elsewhere, there are no other areas of interest, a few tropical waves in the Atlantic but none of concern.

Cyclone Aila

Tropical Cyclone Aila made landfall last night (our time) over Eastern India and Bangladesh killing up to 73 persons and stranding thousands in their flooded villages. Up to 14 inches of rain fell across the area and the storm destroyed nearly 3,000 thatched and mud houses and toppled a large number of trees in nearly 300 villages across India's West Bengal state, said Kanti Ganguly, a state minister. He said 34 people were killed in West Bengal.

The cyclone also caused high waves to hit coastal areas in neighboring Bangladesh, killing at least 39 people, according to Food and Disaster Management Ministry in Dhaka. It said most victims drowned or were washed away by tidal surges.

The cyclone also caused concerns of the world largest tiger populations as flooded rivers burst their banks in a region where 250 tigers live.

Total Rainfall for May 25 2009



Hurricane Preparedness Tips

Continuing with this week's hurricane preparedness theme:

3. If staying with relatives is not an option, consider booking a room in a hotel or motel in another nearby town or state. Make sure to get directions and put them in the car ahead of time. It is easy to forget that piece of paper in the rush out the door. A cheaper route might be to find temporary hurricane shelters. Usually nearby towns not in the direct path of the hurricane will provide these for people in need.

4. Unfortunately, it is unlikely that your pet will have a place in a motel or hotel. Keep this in mind and try to find alternate housing for your loved one until it is safe to return, or check out pet-friendly hotels in your area.

Visitor Map
Create your own visitor map!

Updated: 11:00 GMT le 26 mai 2009

Permalink

Atlantic Quiet But Watching the Bahamas

By: Weather456, 10:37 GMT le 25 mai 2009

United States

The rain continues across the Mississippi Valley as ex-90L dumped several inches of rain across Arkansas, Northern Mississippi and Tennessee during the past 36 hrs. The flood threat continues for parts of the Valley as the river is still expected to swell due these heavy rains. This morning’s satellite and radar imagery showed this system is producing less and clouds and rains and these should diminish as 90L pulls off towards the north. Some areas however may still get locally up to 1 inch of rain.

Because 90L acted as low pressure area across the Southeast United States, warm moist southerly inflow was generated across the state of Florida. In addition, upper level winds were blowing fast and out of the west. This unstable set-up led to the formation of severe weather across the state over the weekend. Several homes were damaged in two Florida neighborhoods Saturday, where residents say a tornado touched down.

The severe weather sent many homeowners scrambling for cover. Several streets were littered with debris, including torn house siding and snapped tree branches.

Caribbean

An area of disturbed weather is located over the Bahamas associated with a broad surface trough of low pressure extending from the Florida Peninsula to Hispaniola. This activity is being further enhanced by upper diffluent flow on the right flank of the negatively-tilted upper trough associated with 90L. The GFS, CMC and ECMWF models develop an area of low pressure by tomorrow and take it towards the north or slightly east thereof due to a ridge building across the Atlantic. Sea surface temperatures remain warm the along the trajectory due the Gulf Stream, vertical wind shear is expected to relax and it is expected to be a moderate warm-core system. However, I would like to see more model support. Based on this, the area will be monitored for development.

Additional scattered showers extend across the Caribbean region due to the advection of moisture in the mid-upper levels. A well define tropical wave is about to enter the Caribbean, based on a westward propagation of a line of clouds, 700 mb winds and PV and total precipitable water loops. This wave is expected to enhanced isolated showers over the Windwards and Trinidad within the next 24-48 hrs with probably higher amounts over the Northeast Caribbean (due to the interaction with upper winds) and South America (due to daytime heating and the ITCZ).





Top 10 Hurricane Preparedness Tips

Continuing with this week's hurricane preparedness theme, here is tip 1 & 2. The remainder will be issued during the course of the week.

1. First, get important papers and special photos in order and secured in plastic. Identification is difficult and time-consuming to replace: so be sure to include social security cards, birth certificates, high school diplomas or GED certificates, titles or deeds to property. Photos of special occasions or loved ones cannot be replaced, so including these is important as well.

2. Think ahead and take video or photos of your property before you leave. This will help later on with any insurance checklist claims for damage that may need to be filed.

Visitor Map
Create your own visitor map!

Updated: 11:10 GMT le 25 mai 2009

Permalink

90L Continues to Dump Rain Over Southeast United States

By: Weather456, 11:42 GMT le 24 mai 2009

Subtropical/Tropical Invest 90L is estimated to have made landfall near the Mississippi/Alabama border yesterday at about 8 am EDT/7am CDT with estimated surface winds of 30 knots and a minimum central pressure of 1005 mb. These winds, however, where not widespread but isolated in strong thunderstorms. Rainfall amounts average about 1 inch with isolated amounts up to 3 inches along the immediate Gulf coast.

This morning’s satellite and radar imagery showed that this low pressure area continues to dump heavy rain across the Mississippi Valley increasing the chances of flooding, Flood watches and warnings have been posted for parts of Louisiana, Arkansas and Mississippi as the river is expected to swell.

Expect this low pressure area to drift west into Arkansas producing up to 2 inches of rain across the area over the next 24-48 hrs.







Elsewhere in the Tropics

Broad upper flow extends from Florida to the Atlantic helping to generate showers across that state, the Bahamas, Cuba, Hispaniola and Puerto Rico. Additional isolated showers are further south across the Lesser Antilles. Showers are heaviest in the subtropical Atlantic between 60W and 40W where a surface trough is enhancing low level lift. Expected this trough to continue to lift into the North Atlantic without any development expected.

A tropical wave is moving along 52W south of 10N based on precipitable water loops. This wave is expected to move into South America enhancing showers across Suriname, Guyana, Venezuela and to a lesser extent, Trinidad.

Dry African dust covers much of the entire tropical Atlantic characterize by a deck of stratiform clouds, subsidence and a hazy appearance seen on satellite imagery.

None of the models are forecasting development within the next week.

Evolution of 90L



Hurricane Preparedness Week

Hurricane Preparedness Week begins today and during the week I’ll be addressing hurricane preparedness from a Caribbean perspective, starting today with the history of notable hurricanes.

History of Caribbean Hurricanes

The Caribbean region remains embedded within the deep tropics and coupled with under developed and developing countries are often prone to the worst of these natural disasters. Of the 6 deadliest Atlantic hurricanes, 5 affected the Caribbean directly, the worst being the Great Hurricane of 1780 which caused thousands of deaths in the Lesser Antilles. This hurricane and many other deadly ones occur in the age where we did not had GOES satellite or buoys, models and the forecasting skill we possessed today. However, even with these, the Caribbean still suffers with Hurricane Gilbert (1988), Hurricane Hugo (1989), Hurricanes Marilyn and Roxanne (1995), Hurricanes Georges and Mitch (1998) and Hurricanes Floyd and Lenny (1999) causing billions in damage across the region despite adequate warning.

There was no period of greater devastation than 2004-2008. In 2004, Hurricane Ivan decimated Grenada, a country which rarely gets struck by hurricanes, and Caymans. Later, Hurricane Jeanne, killed over 3000 in Hispaniola. Less than a year later, Hurricane Emily followed Ivan, passing over northern Grenada as minimal hurricane before hitting the Mexican Yucatan. For the remainder of the season, activity shifted westward with Hurricane Dennis making two category 4 landfalls on Cuba. Hurricane Wilma devastated the resort areas of Cozumel and Cancun after becoming the most intense Atlantic hurricane. In 2007, Hurricane Dean and Felix both made landfall in Central America as category 5 hurricanes, leaving little standing in their way. In 2008, Hurricanes Gustav, Ike, Hanna, and Paloma continued the onslaught in Cuba, the Turks and Caicos, Hispaniola and the Caymans. Hurricane Omar became the strongest storm to affect the Northeast Caribbean since Lenny in 1999.

Other notable Caribbean Hurricanes included, Hurricane David (1979), Hurricane Allen (1980), Hurricane Keith (2000), Hurricane Frances (2004), Hurricanes Stan and Beta (2005), and Hurricane Ernesto (2006).

Preparedness

Despite this apparent concentration of destructive hurricanes, the Caribbean remains resilient and is one of the best responders to hurricanes in the world. Hurricane education is taught at primary (elementary) level and up and to most locals (including myself) hurricane preparedness has become second-nature.

This is still coupled with the lack of warning and preparation due to impoverish nations and isolated villages. Every year, I try to propose some kind of warning system that would warn persons not just in hurricane prone areas, but flood and storm surge prone to leave thus lowering their risk. Another important factor is the deforestation of Haiti which was caused by the Europeans in the 15-18th century. By restoring these hillsides it would lessen the impact of flooding and landslides. Rebuilding yearly does not solve the problem as year after year, there is some terrible news about a tropical cyclone affecting Haiti.

Different Islands, Different Risks

Nor is the risk the same from island to Caribbean island. Bermuda, like Miami, has about a one-in-four annual risk of being affected by a hurricane; the odds for Nassau, Bahamas are about one-in-five.

But the islands of the southernmost Caribbean -- such as Aruba, Barbados, Curacao, Bonaire, Grenada, and Trinidad and Tobago -- rarely get hit by hurricanes: Bonaire, for example, has just a 2.2 percent annual risk of being affected by a hurricane, making your odds about 50-1 against a storm interrupting your vacation.

Likewise, the islands of the Western Caribbean are less likely to be affected by hurricanes than those of the Eastern Caribbean.

The recent Dow Jones Island Index recently ranked Curacao as the Caribbean island least likely to be hit by a hurricane, followed by Bonaire, Grand Cayman, Barbados, and Aruba.

Interesting Fact

The word hurricane comes from the Spanish/Native word huracan. Spanish explorers and conquerors first picked up the word from Taino, an Arawak language from the Caribbean. According to most authorities, the Taino word huracan meant simply "storm," although some less reliable sources indicate that it also referred to a storm god or an evil spirit.

Further Reading:

Hurricanes in the Caribbean
Climatology of Caribbean Hurricanes

Visitor Map
Create your own visitor map!



Updated: 20:35 GMT le 24 mai 2009

Permalink

Tropical Invest 90L to move ashore later today

By: Weather456, 10:44 GMT le 23 mai 2009

Tropical Invest 90L was estimated to be located near 29.4N-87.3W or about 90 nm southeast of Gulfport, Mississippi as of 5 am this morning. Estimated central pressure is near 1005 mb with winds near 35 knots. Radar and satellite imagery showed a steady north-northwest movement. This system is on the verge of becoming a tropical depression with the satellite presentation greatly improving over night as the low level circulation moved under the heaviest convection likely due to 15 knots of vertical shear.

However, the system is running out of real estate as it is forecast to move ashore (near Alabama/Mississippi border) later today, and thus development of a tropical cyclone, if any, has to be now. The main effects of this system, regardless of development, as it comes ashore would be the heavy rain that has already spread across the Gulf coast from the eastern Florida Panhandle to Western Mississippi; isolated gusty winds and some rough seas. 1-3 inches of rainfall expected especially east of where the center makes landfall. Afterwhich, the storm is expected to move inland over the next three days as it transition to an extratropical storm, after dumping rain across the Southeast and Central CONUS.

I’ll have another update later if it becomes a tropical depression or tropical storm.






Earthquake Hits Mexico City

A moderately strong earthquake rocked Mexico City on Friday afternoon, shaking the earth in the sprawling capital.

The U.S. Geological Survey measured the quake at magnitude 5.7, and placed the epicenter near the city of Puebla, about 85 miles southeast of Mexico City. It hit at 2:24 p.m. local time.

The Mexican seismological service measured the quake at 5.9.

People in the city reported the earth and buildings shaking. Thousands of panicked people streamed into the streets as stopped cars snarled traffic. Parts of the city were without electricity Friday afternoon but there were no immediate reports of injuries or damage.

Earthquakes are a frightening experience for the 20 million residents of Mexico City, where thousands of people perished in a massive quake in 1985. The city, built on volcanic ash and clay, is particularly vulnerable to temblors.

Aldo Pontecorvo of the humanitarian agency World Vision said the shaking lasted about 20 seconds. It came out of nowhere and "without any warning," said Pontecorvo, who said he was in his office when the quake struck.

Source: CNN

Visitor Map
Create your own visitor map!

Updated: 10:49 GMT le 23 mai 2009

Permalink

Tropical Update

By: Weather456, 10:24 GMT le 22 mai 2009

Gulf of Mexico

A vertically tilted (upper low northeast of surface low) 1004 mb low pressure area continues to spin slowly northwestward across the Gulf of Mexico causing broad cyclonic flow over much of the Gulf of Mexico. Long-range satellite imagery showed this system has change little over the past 24 hrs with sporadic burst of thunderstorms remaining towards the east the center with dry air west thereof. A QuikSCAT pass from last evening showed winds of 20-30 knots still affecting coastal waters across the SW Atlantic and Northeast Gulf, but to a lesser extent than a few says ago.

This area is moving over 20 knots of shear and 27C sea surface temperatures which is indeed favorable for something of a subtropical nature to form. However, likely due to the dry on the systems west, it is unable to generate sufficient thunderstorms. This system is projected to continue to move towards the northwest, bringing it along the Louisiana coast by tomorrow and due to the asymmetric structure of the storm much of the precipitation (1-3 inches) are expected along the Florida Panhandle, Alabama, Mississippi and eastern Louisiana coasts. In the meantime, development of this feature remains uncertain as in moves into a region of lower shear as it nears the coast but ironically coupled with progressively cooler sea surface temperatures. It will be monitored.





Caribbean

The broad upper low/trough over the Gulf of Mexico extends further south into the Western Caribbean. The upper level divergence ahead of the trough has generated and sustained a large area of thunderstorms just south of Hispaniola. Satellite imagery along with 500 mb analysis revealed mesoscale vortices embedded within this feature and due the spatial size, I’m incline to believe this is a mesoscale convective system (MCS). Under favorable conditions, these mesoscale vortices can develop into tropical cyclones, but it does not seem likely in this situation due to 40 knots of vertical shear across the system. However, the system will be monitored as this shear is expected to let up over the weekend before a jet of 50-70 knots shear is introduced into the region on Monday. Regardless of development this system will continue to produce heavy showers across Hispaniola and Puerto Rico and as the upper trough shifts east, these may spread over the northeast Caribbean.





Elsewhere

Other than these two areas, no other areas of interests in the Atlantic and models are not forecasting development within the next week.

Sometime on the weekend I will post my thoughts on NOAA’s Hurricane Season Outlook and how it compared to my outlook issued last weekend.

Visitor Map
Create your own visitor map!

Permalink

Florida Low Heads For Gulf Coast

By: Weather456, 10:39 GMT le 21 mai 2009

Satellite imagery along with surface observations revealed a broad area of low pressure located over the Southern Gulf of Mexico, moving slowly off towards the west. Shortwave IR imagery clearly outlined an expose low level center with most of the convection displayed towards the east and northeast. This broad area of low pressure continues to interact with high pressure across the Eastern seaboard, resulting in gale force winds across the SW Atlantic, Northern Florida/Southern Georgia and the Northeast Gulf of Mexico. This system dumped up to 10 inches of rain across Florida, over the past several days, caused high winds in excess of 50 knots which downed power lines and tree branches and caused heavy seas up 6 feet which impacted the beaches on the eastern coastline.

Currently, the system remains disorganize but has shown some signs of improvement. This, however, may change as the system is expected to move west into more favorable conditions in the next 24-48 hrs with low shear expanding due the broad upper low the system is embedded in and warmer sea surface temperatures in the central Gulf of Mexico. After which, the storm will curve northwestward then north under the influence of the aforementioned anticyclone along the east coast, which should bring it along the Louisiana/Mississippi coast by Saturday as a weaker system, and because of the asymmetric structure of the system, most of the rain and wind is expected northeast of the center over the western Florida Panhandle, Alabama and Mississippi.







Elsewhere

The diffluent flow east of the broad upper low over the Gulf of Mexico is generating a large area of disorganize showers between 80W and 60W which includes the Bahamas, Jamaica, Cuba, Hispaniola and Puerto Rico. With additional showers spreading over the Northeast Islands later today and tomorrow. Global models continue to predict the formation of a low pressure area northeast of the Bahamas on Sunday and thus the area will be monitored.

Hurricane Season Outlook

NOAA is expected to issue thier 2009 Hurricane Season Forecast at 11 am according to media reports.

Visitor Map
Create your own visitor map!





Updated: 14:46 GMT le 21 mai 2009

Permalink

Wind, Surf, and Heavy Rains affecting Southeast United States

By: Weather456, 10:21 GMT le 20 mai 2009

Tropical Invest 90L maybe gone, but the system that absorbed it is dropping copious amount of rain across state of Florida, generating gusty winds and heavy surface along the SW Atlantic coast and northeast Gulf coast. There have been numerous high wind, high surf and flooding warnings posted for areas along the Florida Atlantic coast. Refer to your local officials in regards to these.

This morning’s surface observations indicated that a broad area of low pressure is centered on a 1007 mb low in the extreme southeastern Gulf of Mexico with satellite imagery showing a band of deep convection curving across the Southern Bahamas, Turks & Caicos, SW Atlantic, over Northern Florida and into the NE Gulf of Mexico. Lightning data and radar imagery revealed heavy thundershowers embedded within this band as far south as Cuba. Water vapor imagery indicated a dry slot intrusion sweeping south of the heaviest activity leaving fair weather across much of Cuba, Bahamas and Florida Keys.

The pressure gradient between this low pressure area and high pressure off the US East Coast is generating a swath of northeast gales which is impacting the Atlantic coast of Georgia and Northern Florida generating seas near 10 ft over the adjacent waters.

All of the reliable computer models are in agreement that this feature will track west over the next day or two and it has already done so, as it previously located over Southern Florida. The CMC strengthens it as it moves towards Louisiana. The GFS also moves it towards Louisiana but dissipate offshore and all other models, dissipate this feature in the western Gulf of Mexico. The models are hinting on a jet of upper level winds on the crest of a ridge over the Eastern Pacific to be introduced into the region 72 hrs causing high wind shear. However, sea surface temperatures are warm, anomalously warm, in the Central Gulf and there is a small window of low shear before then. Cyclone phase diagrams already show a shallow warm-core system, so there is still the possibility (30%) of a subtropical depression developing within the next 3 days. The system will be monitored through then.



It’s not All Over

Most of the models are also hinting on the development of a feature along the tail end of the band of convection just north of Hispaniola. Sea surface temperatures are not particularly conducive for development, but wind shear is expected to drop to marginal values and thus the area will be monitored.

Non-Tropical Low

The non tropical low in the north Atlantic near Bermuda has change little over the past 24 hrs and cyclone phase diagrams or satellite imagery are not showing any signs of subtropical development. This 1014 mb low pressure area is expected to weaken over the next 48 hrs and this will be the last time I will speak of it unless it shows some sign of organization.

Africa

Clusters of convection are across the West African continent but none of the available data suggest any wave like features. There maybe a African easterly tracking across the continent in 1 week’s time.

Eastern Pacific

An area of convection is along the ITCZ that has increase in intensity and spatial coverage over the past 24 hrs. This system will be monitored over the next several days for tropical development.



==================================================================================================











Bouy Observations

Visitor Map
Create your own visitor map!



Updated: 18:08 GMT le 20 mai 2009

Permalink

Battle of the Lows

By: Weather456, 10:53 GMT le 19 mai 2009

Broad area of low pressure extends from the Southeast Gulf, across South Florida and the Bahamas, with two low centers near the Florida Keys and the other over the Central Bahamas. Shortwave imagery and an ASCAT pass was used to identified the location of the latter low. Water vapor imagery is showing how the two lows are battling with the low over the Keys appear to be winning, as the cyclonic flow around its coupled upper level low is providing 30 knots of shear over the Bahamian system, making it highly disorganize. At this point, I am uncertain whether the original system 90L will survive or continue to merge/absorbed with/into the low over the Keys as it moves northwestward. But if this keeps up, the latter scenario seems possible, and that is the scenario I expected last night.

Currently, the two systems are producing a large area of convection with heavy showers and thunderstorms expected over the Bahamas and Florida. The low pressure area that develops will most likely be extratropical at first but transition to subtropical over wamer waters and possibly lower shear and drift west over the Florida Peninsula and Gulf as the front exit and high pressure builds over the Southeast CONUS. The effects of this system over Florida and adjacent coastal waters will be rain and wind. Due to the pressure gradient, gale winds maybe felt across Florida, Georgia, the coastal SW Atlantic and Northeast Gulf.

Tropical Moisture

The deep layer trough that accompanied the frontal system dipped far into the Caribbean, and interacted with convection along Central-South America, producing a swath of moisture that produce showers and isolated thunderstorms over the Northern Caribbean, with some locals picking up several inches over the past 48hrs. This moisture was then enhanced by local heating, tradewind convergence and a frontal system draped north of the region, making for some heavy showers at time.

Tropical Waves

A tropical wave is along 50W, south of 12N moving west near 10-15 knots based on precipitable water loops, and cyclonic turning seen in the low level cloud decks on infrared imagery.

Non-Tropical Low

This area has change little over the past 24 hrs with this morning satellite images showing little convection associated with this feature. The system will continue to be monitored but is nearing the end of its life cycle.





Visitor Map
Create your own visitor map!

Updated: 11:04 GMT le 19 mai 2009

Permalink

Tropical Invest 90L

By: Weather456, 00:01 GMT le 19 mai 2009

Tropical Invest 90L

The tropics are stirring this evening with newly designated Tropical Invest 90L, the first area of disturbed weather in the tropics for the 2009 Hurricane Season. The area of disturbed weather appears to be an area of low pressure centered near 22N/76W or over the Central Bahamas moving off towards the north or slightly east of there based on visible imagery. Visible imagery from this afternoon also showed a mid-low level turning associated with the system with clusters of showers to the north and east. The area remains disorganize due to 20 knots of westerly shear and I cannot find much evidence that the mid-low level turning is closed. Sea surface temperatures are 26.5C but just on the borderline of tropical cyclone development though this system maybe become extratropical or subtropical, requiring less heat content. Because wind shear is forecast to remain near 15-20 knots, development seems slow and uncertain as the area moves towards the north-northwest over the next 24 hrs.

Now here comes the action. There is another vertically stacked low at the base of frontal system in the southeast corner of the Gulf of Mexico which is expected to move towards the northeast. This motion would actually bring it into contact with the low over the Bahamas, and because the low over the SE Gulf is coupled with an upper level low overhead, it may provide some low wind shear for either one or both systems. Since these two systems have some non tropical characteristics, I am more inclined to believe a merger rather than rotation around a common point if the two are brought together. That being said, expect a broad area of low pressure from the SE Gulf across Florida and into the SW Atlantic over the next 3 days if they do come together as there is still the possibility the Bahamian system shifts northeast, out to sea.

This low pressure area may then develop and drift west over the Gulf as the front exit and high pressure builds over the Southeast CONUS. The effects of this system over Florida and adjacent coastal waters will be rain and wind. Due to the pressure gradient, gale winds maybe felt across Florida, Georgia, the coastal SW Atlantic and Northeast Gulf.

I will the remainder the tropics and African coast in the morning update. There have been copious amount of rainfall over the Caribbean yesterday and today and I will review these tropical rains tomorrow and discuss or maybe second wave. In addition, we still have our non tropical low out in the North Atlantic that is still being monitored.

72hr Rainfall


<

Visitor Map
Create your own visitor map!




Permalink

Subtropical Sandwich Anyone?

By: Weather456, 09:20 GMT le 17 mai 2009

2009 Hurricane Season Outlook

Most of the reliable global models continue to hint development of an extratropical or subtropical feature later next week either in the NW Caribbean, SW Atlantic or SE Gulf of Mexico. Currently there is a suspected surface trough south of Cuba (75W-80W) that continues to interact with cyclonic mid-upper level winds to produce moderate to strong showers and thunderstorms over the NW Caribbean, Cuba and Jamaica that has increase in organization and spatial extent. This trough is expected to track towards the northwest, roughly parallel to the coast of Cuba, becoming more amplified as a surface low builds towards the surface over the next several days. This trough/low is then expected to interact with an advancing surface cold front. As the frontal trough secludes, there becomes the possibility that a subtropical cyclone may form under a broad upper low. Currently, there are little signs of a surface low as of yet, with a 5-knot westerly wind reported at Kingston, Jamaica but nothing on a synoptic scale.

Most of the models do take this feature into a region that is marginally favorable for development with warm sea surface temperatures, modest to low shear (as it becomes enveloped within a negatively tilted upper trough/low) and moisture.

While development certainly now seems possible, the trick now, is forecasting where it will go. What is expected to help pull this feature north is the advancing frontal trough. For now the system will move towards the northwest, riding the periphery of a quasi-stationary high pressure in the Western Atlantic and by the time the trough arrives, it should be near the western tip of Cuba. However, the 00Z GFS and UKMET have the system much further east, across Cuba and moving east of Florida, then turning west across the state. The remaining model solutions – CMC, NOGAPS and ECWMF has the system in the SE Gulf of Mexico or Florida Straits, remaining west of Florida. Current and forecasted surface-500 steering flow seems to support the latter three but due to the system being further south and east than previously thought, the GFS and UKMET solutions maybe satisfied. Regardless of this inconsistency, the consensus remains that the system will eventually make its way into the Gulf of Mexico.

The major impacts of this potential system will be the rain, wind and surf. Regardless of whether the system is extratropical or subtropical, the asymmetric rainfall pattern, track and speed implies rainfall totals near 3-5 inches (10-15 cm) across some parts the Florida Peninsula and Panhandle. The tightened pressure gradient between the forecast low and high pressure over the Atlantic implies some possible gale force winds. Please refer to you local weather office.

In summary, there is 50% chance something develops next week with a 30% chance of it being subtropical in nature.



A non tropical low pressure area just east-northeast of Bermuda may also want to transition to subtropical. The latest satellite imagery show bands of cloudiness wrapping and rotating closer to the center as the system remains quasi-stationary. QuikSCAT also showed the gale force winds much closer to the center of this system. In addition, the cyclone has begun to seclude from its associated fronts which implies a feature possibly becoming subtropical. However, cyclone phase diagrams continue to hint this system remains neither warm-core nor cold core and it doesn’t seem to be forecasted to become warm-core. Despite this, the system will continue to be monitored for development.



There are no tropical waves analyzed at this time in the tropical Atlantic or over the mainland of Africa. The first tropical wave that emerged over the waters last week is not being analyzed by the Tropical Prediction center but based on continuation, TPW loops and low level infrared winds, the feature is most likely located near 40W, south of 10N.

Visitor Map
Create your own visitor map!

Updated: 17:07 GMT le 17 mai 2009

Permalink

2009 Hurricane Season Outlook

By: Weather456, 10:51 GMT le 16 mai 2009

Tropical Update for May 16 2009

2009 Hurricane Season Outlook

The 2009 Atlantic Hurricane Season is expected to be slightly above average with 12-14 named storms, 6-7 hurricanes and 3 major hurricanes. The areas of most concern are the Northern Caribbean from the Leeward Islands to the Bahamas and the East Coast of the United States. The Cape-Verde season is not expected to be as active this year with development closer to home, mainly north of 20N and west of 50W.

Forecast Uncertainties

The 2009 displayed many challenges in forecasting some of the indicators as there were contradicting information displayed by climate models. The information displayed in this report was manly based on climate data gathered over the past month incorporating analog years and some model data.

Main Indicators

ENSO/Vertical Wind Shear
Rainfall Patterns over Sahel and the Subtropical East Atlantic
The North Atlantic Oscillation (NAO) and Mean Sea Level Pressure (MSLP)
Sea Surface Temperatures
Continuation of Above Normal Activity since 1995 and New Tools and Technology

Overview of Indicators

El Niño-Southern Oscillation (ENSO)

During El Nino, high SST over the eastern Pacific causes more deep convection there. The resultant outflow aloft enhances westerly wind shear over the Caribbean and western equatorial Atlantic. Consequently, the 200 mb anticyclonic flow necessary for tropical cyclones to develop is reduced. During Neutrals and weak to moderate La Nina, low SSTs over the eastern Pacific suppress deep convection there. The resultant subsidence enhances rising motion and weak to moderate upper level easterlies over the Tropical Atlantic Summer, which favors tropical cyclone development.

Rainfall Patterns over West Sahel and the Subtropical East Atlantic

West Africa represents the birth place of most Atlantic tropical cyclones. It is also the origin of the West African Dust outbreaks known as the Sahara Air Layer. Wetter than normal conditions over Sub-Sahara Africa indicate wetter and more convective tropical waves increasing the temperature gradient between the sea surface temperature and the 700 mb wave axis and enhancing convection. Wetter than normal conditions also indicate reduce dust phenomena during the season. Drier than normal conditions produces hotter waves at 700 mb and as they move over the cooler sea surface temperatures, this creates a temperature gradient that reduces convection. Drier conditions over West Africa means enhanced African Dust.

The North Atlantic Oscillation (NAO)/MSLP

The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low. The Negative NAO index phase shows a weaker than normal subtropical ridge center and weaker than normal Icelandic low. A stronger than normal ridge lowers SSTs due to increase evaporational cooling of winds blowing over the water and due to decrease southerly flow. A weaker than normal ridge implies more ridging in the Central Atlantic and warmer sea surface temperatures over the Atlantic due to increase southerly flow and less cooling effects by evaporation.

In addition to the effects on SSTs, weaker trades favor tropical cyclone activity (negative NAO index) while stronger than normal trades suppresses tropical cyclone activity (positive NAO index). This is because, the circulation needed for tropical waves and other disturbances to be classified as tropical depressions are disrupted under too much northeast wind flow.

A stronger than normal high implies above average surface pressures while a weaker than normal high implies lower than average surface pressures.

Overview of Remaining Factors

Tropical cyclone activity is enhanced (suppressed) when mean sea level pressure is below normal (above normal), vertical wind shear is below normal (above normal), and sea surface temperatures are above normal (below normal).

Continuation of Above Normal Activity since 1995 and New Tools and Technology

Since 1995, Atlantic tropical cyclone activity has been in upward swing.

Depiction of new monitoring and analysis technologies (advanced microwave sounding unit tropospheric temperatures [Brueske and Velden, 2003], QuikSCAT [Atlas et al., 2001], and the cyclone phase diagram analyses [Hart, 2003]) have increased Atlantic tropical cyclone counts by about one additional system per year.

Summary of Conditions



El Niño-Southern Oscillation (ENSO)/Wind Shear

The La Nina that developed last winter continued to weaken through April 2009 and now the transition to neutral is underway. There is some model consensus that neutral conditions will develop and persist through this summer with a weak El Nino developing late this year. It should be noted that if El Nino develops this summer, the effects will lag a good 2-3 months behind, so this indicator is somewhat clear-cut and I’m confident about it. There were signs of this across the tropical Atlantic as vertical shear as near to below average for April 2009 along the subtropical jet axis and an ENSO episode of -0.5.

Rainfall Patterns over West Sahel and the Subtropical East Atlantic

African easterly waves vary interannually, and these variations have been found to have an impact on the seasonal hurricane frequency. Increases in rainfall over the western Sahel have been associated with more frequent and stronger waves, and with the occurrence of more intense Atlantic hurricanes.

The best indicator of the variability is the rainfall between November and May before the upcoming hurricane season which has been below average over Sahel. I do not think we will have an increase number of strong waves this year as we saw in 2008 and hence a less active but average Cape Verde Season due the below normal rainfall and cooler sea surface temperatures off the coast. However, despite the increase in tropical wave variability in 2008, we only saw two Cape Verde Hurricanes. This simply means, regardless of any year, we see an average of 1 Cape Verde tropical cyclone but that statistic should not affect the overall numbers this year.

The Subtropical Atlantic was slightly wetter than normal indicating not much dust events this past spring but one should remember than the Saharan Air Layer (SAL) events peaks in July.

The North Atlantic Oscillation (NAO) and Mean Sea Level Pressure (MSLP)

There was no doubt that April 2009 saw a positive phase in the NAO with a stronger Azores High and deeper Icelandic Low. Average MSLP was also above average for much of the Atlantic basin with trades averaging above normal.

This weakening positive phase should continue into the first two months of the hurricane season but eventually transition to negative during August and September then return positive in the latter two months. This has average out the oscillation as neutral with a positive bias.

A stronger than normal subtropical ridge over the Azores increase the trades which whips up dust and advect it into the eastern Atlantic, and thus it effects should be seen mainly in July. However, the degree of recovery by the Atlantic during August and September will determine how active the tropical Atlantic will eventually be.

Sea Surface Temperatures

Stronger than normal trades earlier this year implied increase evaporational cooling in the tropical Atlantic but downwelling and warming in the West Caribbean and Gulf of Mexico and just off the east coast. This is the basis on which I based the development areas in the introduction above and explained the temperature anomaly pattern being observed in April 2009.

Despite this cool anomaly, I think that sea surface temperatures will rebound during the hurricane season, leading up to the peak and with the NAO reversing; it can be assumed that sea surface temperatures and the Tropical Cyclone Heat Potential (TCHP) will warm to their climatological means.

In addition we must consider a number of factors when predicting this factor and its effects on the hurricane season:

1) The Eastern Atlantic is naturally cooler due to the cold current, constant trades and most importantly dust which imbalances the natural heat budget of the tropical Atlantic.

2) Most hurricane seasons, despite their activity only about 2-3 storms form east of 40W.

3) The Phase of the NAO is expected to change leading up to the peak months which implies less of an impact on SSTs by the trades and again, the degree of recovery will affect the overall activity.

Summary

I have summarized the above forecast by dividing the Atlantic into five regions below.



Regions 1, 3 and 4 – Average development but more uncertainty with storms moving into region 1.
Region 2 – More random development and tracks
Region – 5 – Average to below normal development

Analog Years

I have identified three years in the past that have the conditions observed in April 2009 and these three years had similar conditions in June, July, August and September similar to what is expected during the 2009 hurricane season. Those are 1996, 1976 and 1951 and most of those years described the type of storms, their origins and path of what may possibly come in 2009.

The Forecast Numbers

Based on the above information, adjustments to the normal seasonal average can be made. An average hurricane season based on over 150 years of records is 10.0 named storms, 6.2 hurricanes and 2.7 major hurricanes.

My current forecast includes a plus factor for ENSO, sea surface temperatures and continuation of above average tools this year with NAO being an uncertainty and Western Sahel rainfall a non-contributing factor. The current forecast calls for 12-14 named storms, 6-7 hurricanes and 3 major hurricanes.


Figure 1 & 2: Sea surface temperature anomalies for Nino regions 1, 2 and 3.4 (Eastern Pacific and Central Pacific) up until January 2010 from NOAA’s CFS model. The red lines indicate the boundary of typical neutral-episodes conditions.


Figure 2: Upper left: Easterly wave variations during wet versus dry years in Western Sahel, upper right: 180-day rain accumulation % of normal showing drier than normal conditions along Western Sahel, lower left: probability rainfall forecast for Sahel for the peak months of July – September and lower right: TRMM rainfall anomalies over the past 30 days showing average rains over the Eastern Atlantic Ocean.


Figure 3: Mean sea-level pressure (MSLP) anomalies for July and September showing a positive NAO in the former month and a negative NAO in the latter.


Figure 4: Global blended SST anomalies showing near average sea surface temperatures for the North Atlantic Basin and the El Nino Region for July, August and September. Fro the tropical oceans, this is an average of several forecast models.


Figure 5: (a) Surface marine observations available in the Atlantic basin around 1200 UTC for a typical day in 1907. These observations were based entirely on ship measurements. (b) Same as Figure 6a but for a typical day in 2007. These data include moored and drifting buoys, QuikSCAT, as well as ship observations. (c) Depiction of new monitoring and analysis technologies (advanced microwave sounding unit tropospheric temperatures [Brueske and Velden, 2003], QuikSCAT [Atlas et al., 2001], and the cyclone phase space analyses [Hart, 2003]) that have increased Atlantic tropical cyclone counts by about one additional system per year.

2008 Hurricane Season Outlook
2008 Hurricane Season Forecast Verification

Visitor Map
Create your own visitor map!

Updated: 00:00 GMT le 24 mai 2009

Permalink

Tropical Update

By: Weather456, 10:40 GMT le 16 mai 2009

Atlantic

A non tropical occluded low pressure area continues to spin east-northeast of Bermuda with little change over the past 24 hrs with satellite imagery showing bands of showers in and around the system’s circulation. This system remains embedded within a large upper low providing a region low vertical shear over the system. Sea surface temperatures are on the borderline for subtropical development. Last night’s QuikSCAT pass revealed an impressive low level circulation with calms at the center and gale force winds on the periphery especially where the pressure gradient is tightest between it and the blocking ridge. The system is expected to transition into a non-frontal flat thermal core system (neither warm core nor cold core) and during this time, there’s a slight chance (25%) that it could transition to a subtropical system. This system will continue to be monitored.

Most global models continue to develop an area of low pressure over Southeast Gulf of Mexico and latest model runs from 00Z have made much more sense than yesterday. The models are forecasting genesis along the base or tail end of a frontal trough later next week. The latest shear maps show a larger region of modest-weak vertical shear and this coincides with broader upper trough being forecasted and some warm sea surface temperatures. Based on this information, we should be inclined to believe the models because what are the chances that four global models (NOGAPS, GFS, ECWMF and CMC) hinting on development in the same region and time frame. However, it is still too early to tell what will form and the outcome but anything forming will take some time to get its act together. I still give this area a 30% chance of developing. Anything forming will be influenced by high pressure over the Eastern CONUS and West Atlantic.

Eastern Pacific

Convection along the ITCZ continues to expand this morning and QuikSCAT imagery showed a sharp wind shift along a trough along the ITCZ. This maybe starting point of anything that tries to develop with low upper winds, outflow and warm sea surface temperatures. The global models appear to be forming another area further west at later time frame. The region will continue to be monitored.






Permalink

Tropical Update/Eastern Pacific Season Begins

By: Weather456, 10:39 GMT le 15 mai 2009

Eastern Pacific

Today marks the start of the 2009 Hurricane Pacific Season which runs through November 30. An average hurricane season defined by NOAA includes 15 named storms, 8 hurricanes and 4 major hurricanes. I am expecting a near-to slightly above average season. Currently there is an area of disorganize showers along the ITCZ in the central Eastern Pacific that some models continue to develop this weekend. Sea surface temperatures are warm and wind shear is expected to let up due the expansion of an upper ridge over the area. However, due to the stable air to its north, it isn’t expected to be a significant system if it develops as that is where it is likely to track. The area will be monitored.



Tropical Atlantic

Some global models continue to forecast the development of a subtropical cyclone off the coast of Florida early next week. Genesis begins as a mid-upper level low develops across the Southeastern Gulf from either the existing upper low over Cuba or a cut-off circulation at the base of an advancing frontal trough. These systems tend to generate some type of surface reflection under the instability east of the circulation and in this case it is a surface trough.

In the meantime, a cold front is advancing south and interaction with this feature along with the help of sea surface temperatures may help generate some convection, heat and eventually low pressure at the lower levels. The global models, despite their consistency in developing this feature are spilt on the point of genesis which can range from the NW Caribbean, SE Gulf or SW Atlantic.

The system briefly moves towards the northeast but steered back towards the west due to high pressure to its north. This high pressure system plays a role in helping to generate some potentially strong winds over the Florida Peninsula causing this potential system to be more of problem than a benefit especially if it becomes enveloped in dry air. The system continues west across the Gulf of Mexico at the end of model cycle and that part the models agree on.

Due to its genesis and nature the system is expected to be subtropical. The strength of this system depends on where it forms, the degree of land interaction as oppose to exposure over warm waters and vertical shear. The latter is expected to be modest. I’ll remain at 30% chance of development for now. Regardless of development, there is good chance for moisture to spread across the Peninsula.



Eastern Atlantic

A very weak tropical wave is moving along 26W south of 10N based on continuation and precipitable water loops. This feature has been dropped by the Tropical Prediction centre most likely due to its lack of convective signature but for the meantime, can still be tracked using low level fields.

Evening Update

A non-tropical occluded low pressure system is located just to the east-northeast of Bermuda. This feature remains embedded with a large cut-off upper low that has become trapped by bridging high pressures. Satellite imagery show bands of showers to the east and northeast of the low pressure system with QuikSCAT showing gale force winds mainly to the north where the system is interacting with high pressure. Cyclone phase diagrams show the system is on the borderline of a shallow warm-core system moving over 20-23C waters. This system is expected to meander over the area moving into gradually warmer SSTs at time. The large upper low that envelops the system may help to create some low vertical shear over system allowing for some organization of cloud clusters and gradually tightening over the low level wind field. The area will continue to be monitored for subtropical development. This is the same area that was being forecast to develop across the Atlantic for several days.

My view has change little regarding the development of the development of the subtropical cyclone next week except models are in little more agreement as to where it will develop and they have later intiation date maybe due to the fact that subtropical cyclones take more time to get going than thier tropical counterparts. A more detailed update tomorrow morning.



Visitor Map
Create your own visitor map!

Updated: 23:11 GMT le 15 mai 2009

Permalink

Tropical Update & More

By: Weather456, 10:35 GMT le 14 mai 2009

Tropical Atlantic

A cold front continues to track its way west across the Atlantic and most of the global models continue to forecast the development of non-tropical low pressure area in the Central Atlantic that would become trapped by bridging highs causing it to meander and eventually dissipate. This system should be relatively weak forming over 20-23C waters and modest vertical shear. The system is expected to transition to a shallow warm-core system as it reach the end of its life cycle and thus will be monitored.

An upper level ridge is located over Eastern South America extending into the Eastern Caribbean while another upper level ridge is located over the Eastern Pacific and Mexico. These two upper level ridges have induced an upper trough axis from 10N/85W to 25N/75W with an upper level circulation over the Central Bahamas. These upper level features are continuing to interact with a surface trough near 72W to produce scattered showers and possible isolated thunderstorms over Puerto Rico, Hispaniola, Cuba and the Southern Bahamas. There are some indications that this may play a role in the initiation of a possible subtropical cyclone early next week as it interacts with the southwesterly flow ahead of an advancing trough.

Global models continue to forecast development of a subtropical system early next week or in about 4 days. The models are showing a surface low pressure system being generated by southwesterly divergent flow aloft somewhere in the SE Gulf or Western Caribbean Sea and eventually moving off towards the northeast across the Western Cuba and the Florida Peninsula before re-curving back towards the west due to high pressure either in the Eastern Gulf or over the SE United States. During this time, the cyclone is expected to become associated with a cut-off upper low making it subtropical. While upper level winds are not expected to relax much over the upcoming days, the overhead upper low is expected to provide some level of favorable shear over the system. Models have been consistent with this area and it will be monitored. In all, I’ll give this a 30% chance of development for now due to vertical shear and the degree to land interaction as oppose to expossure over the Gulf Stream. Regardless of development, moisture is expected to spread across the Bahamas, Cuba and the Peninsula later this week and into next week.



First Official Tropical Wave of 2009

The first official analyzed wave of 2009 rolled off the coast early yesterday, 13 May 2009. The wave is now located near 20W south of 14N based on Total Precipitable Water loops and numerical models. This wave has little signature on satellite imagery with little associated convection except for some shallow clouds. Yesterday I was asked the question how I predicted that a wave would form in the Eastern Atlantic days before and the answer is simply:

The wave did not form in the Eastern Atlantic, I was tracking it over the continent and the only prediction I made was when it would emerge over the Eastern Atlantic.

No development is expected. Below is how this year stacked up against others when it came to first tropical waves.



Tropical Update Video by W456



The 2009 Pacific Hurricane Season begins tomorrow, My 2009 Hurricane Season Outlook will be issued the following day and on Sunday my 16-31 May Outlook.

Visitor Map
Create your own visitor map!

Updated: 17:22 GMT le 14 mai 2009

Permalink

Wave or Not to Wave

By: Weather456, 10:46 GMT le 13 mai 2009

Tropical Atlantic and Africa

A cold is draped across the Southwest Atlantic with a band showers extending just east of Florida/Georgia into Atlantic beyond 35N/55W. Most, if not all, of the global models continue to hint on development of a non tropical low pressure at the tail end of this front later this week that is expected to become trapped by bridging high pressure centers. At one point, the isotherms encircle the low pressure which indicates a barotropic system but over waters near 23C it is most likely a barotropic cold core system. Just to get your reference, a mature tropical cyclone is a barotropic warm-core system and a typical extratropical system is a baroclinic system. This situation will continue to be monitored.

It was pouring here in the islands just hours ago as a surface trough of low pressure continues cause speed convergence and moisture across the islands today. This moisture has since spread to Puerto Rico, the Virgin Islands and parts of the Dominican Republic. This feature is expected to continue towards the northwest, spreading over Cuba and possible the Bahamas over the remainder of the week. The GFS has been hinting on developing this system as it interacts with a surface cold front at the beginning of next week. Other models are in consensus that surface trough will move towards Florida but with little development but rather along the front and one model, the NOGAPs, has trough further west in the Gulf of Mexico. Vertical shear is not expected to relax much which causes tropical cyclogenesis to seem unlikely. However, I will continue to monitor the situation as models are ambiguously hinting on development somewhere in this region.

A surface trough or weak tropical wave sits along the African coast near 18-19W with little associated convection. Much of the available data still supports a tropical wave but this feature continues to lack any significant convective signature. Upper air observations from Dakar, Senegal showed a surge of easterlies at 600 mb accompanying this feature which is a characteristic of tropical waves but little wind shifts observed. Tropical waves do emerge off the coast without much convection but it will be understandable if is this feature does not survive the oceanic environment. This is one of the first official mentions of a tropical wave for the season.

Eastern Pacific

Most of the global models are still forecasting some type of development along the ITCZ. The area will be monitored as the region seems somewhat favorable for cyclogensis.





Afternoon Update

A surface trough or tropical wave near 70W moving towards the west-northwest continues to generate scattered showers across the Leeward Islands, Puerto Rico and Hispaniola this afternoon. The 12Z GFS is forecasting a Barry-like weather system and looking at the rain pattern relative to the LLCC, the system is being sheared by 15-20 knots southwesterly upper winds probably ahead of an advancing upper trough. This system appears somewhat subtropical but there is the potential for tropical development. All this occurs in 126 hrs around Sunday-Monday. The genesis is likely tied to some interaction between the aforementioned surface trough and a cold front. Regardless of development, moisture is expected to spread across Cuba, the Bahamas and then Florida into the remainder of week and weekend.

The first official African Easterly Wave (African Tropical Wave) is near 19W-20W south of 12N moving west near 10-15 knots with little or no associated convection.



Visitor Map
Create your own visitor map!

Updated: 17:48 GMT le 13 mai 2009

Permalink

Tropical Update

By: Weather456, 10:42 GMT le 12 mai 2009

Tropical Atlantic and Africa

Broad upper ridging continues to enhance scattered showers and thunderstorms along the ITCZ over the Eastern Pacific, Central America, NE South America and the Southwest Caribbean. This upper level flow continues to stretch over the Caribbean basin and into the tropical Atlantic where it intersects a surface trough moving across the NE Caribbean resulting in scattered low level moisture across the area. Expect this moisture surge to spread west across Puerto Rico and Hispaniola over the next 24 hrs.

A developing frontal system just offshore the United States east coast with a low pressure area at 33N/71W is generating showers and possible thunderstorms across the Atlantic between 70W and the coast, north of 25N. This is the non-tropical low pressure that was being forecasted by most of global models. It is expected to deepen as it moves off towards the north and east.

In the wake of this system, global models continue to develop a low pressure area at its tail end that is expected to become trapped, stalled and eventually dissipate. During this time this area has a low chance of becoming subtropical but will be monitored.

A wave-like feature is now exiting the African coast and much of the available data suggest a possible wave axis. Satellite imagery show little associated convection but signs of cyclonic turning. The GFS among other models support a wave axis and it is forecast to maintain itself as it emerges over the more stable oceanic environment.. This area is interesting enough and I will continue to monitor the area.



Eastern Pacific

Three models (GFS, CMC, and NOGAPS) continue to forecast the development of a weak low pressure area somewhere along the ITCZ across the Eastern Pacific later this week. Wind shear is expected to become more favorable over the next couple of days and their seasons commences on Friday. I will continue to monitor this situation.

Visitor Map
Create your own visitor map!

Updated: 18:02 GMT le 12 mai 2009

Permalink

Tropical Update

By: Weather456, 11:09 GMT le 11 mai 2009

Good morning to all,

The tropics remain quiet this morning with high pressure in control over most of the region. Broad upper ridging over the Caribbean helping to enhance showers and thunderstorms over the ITCZ region with a moisture plume extending over the region into and across the tropical Atlantic.

Most global models continue to forecast the development of a non-tropical low pressure area off the US East Coast in the next 24-48 hrs which is expected to move off towards the north and east. As this system tracks over the North-Central Atlantic, the GFS is forecasting a system to develop along the tail end of the associated frontal boundary and become trapped by bridging high pressure systems. Consequently, the system is expected to stall and meander for a couple of days and eventually dissipate. During this time, there isn’t any hint that the system will become subtropical but the system will be monitored incase it tries to.

An area over mainland Africa is suspected to be a tropical wave but will have to be confirm after it emerges over the waters, as the GFS forecasts.



Eastern Pacific

A surface trough along the ITCZ has continue to generate a large area of deep convection over the Eastern Pacific and the GFS and some other models are hinting on development of a weak low pressure system in this vicinity. I will continue to monitor the area as wind shear is forecast to be marginally favorable.



Visitor Map
Create your own visitor map!

Permalink

Tropical Update/Flooding in Brazil

By: Weather456, 12:33 GMT le 10 mai 2009

Tropical Atlantic-African Coast

Currently there aren’t any areas of interest within the Atlantic basin. Both the 06Z NAM and GFS continues to develop an area off the US East Coast but this feature will most likely be non-tropical due to a number factors discuss yesterday and the fact that it is expected to an asymmetric cold-core system. In addition, the system will form on the northeast flank of the subtropical ridge which indicates quick movement off towards the northeast once formed.

In the wake of the system above, the GFS is also spinning up a next system south of blocking ridge just offshore the Canadian Maritimes on Saturday or in 138 hrs. This feature appears non-frontal and trapped for several days before dissipating. This system however looks non-tropical but of interested to see if it manages to acquire some subtropical characterizes while meandering in the Northwest Atlantic.

The GFS continues to forecast the emergence of a wave-like feature this week and this morning’s visible satellite imagery showed an area of convection along the African coast that coincides with the GFS initiation. I’ll be watching this feature as it continues west.

Major Flooding In Brazil

Yesterday, while investigating the ITCZ using the Tropical Rainfall Measuring Mission satellite (TRMM), I notice an area of anomalous rainfall over Northeast South America, that was even higher than the rainfall of Typhoons Kujira and Chan-hom combine. It is typical for this type of rainfall in spring across South America as the ITCZ begins to shift north into the rainy season region causing two sources of rainfall. But according to media reports, it has been raining non-stop for 2 months, causing major flooding and landslides across northeast Brazil leaving 500,000 homeless and 31 dead.


At least seven states, most in the Amazon region, have been affected by the rains, which have battered the region for several months; regional civil defense departments told the Associated Press. Worst-hit is the state of Maranhao along the Atlantic coast, south of the mouth of the Amazon River, and Santa Catarina.

Around 218 000 people have forced to leave their houses due to swollen rivers and landslides which have blocked roads and hinder rescue attempts. The lucky ones have escaped in boats, but the rest have had to walk through waist-deep water infested with rattlesnakes and anacondas.

An aid operation has begun and the army has already evacuated thousands of people from towns that have been cut off. But some remote communities have been isolated for days with little food or clean water because rescue planes cannot land on the water-logged ground.

Those who have made it to dry land have set up camp anywhere they can, taking shelter in gyms, stables and even an abandoned hospital.

In Mananhao, the state worst hit, aid supplies are piled up but there is nobody to distribute it, and the rivers there are still rising by as much as 30cm a day.

Joaquin Godim, from Brazil's National Water Agency, said: "We don't know yet, but this could end up being the worst flooding ever in the region."

Thirty-six people have died and thousands are in desperate need, with the authorities concerned now on a major health crisis.



TRMM based measurements show an average of 20 mm per day over the past month, which seems minute but that is equivalent to 23.4 inches for the past month and that is 6 months of rainfall for us here in Saint Kitts, Miami and Rio De Janeiro in Brazil. This rainfall anomaly has been plus 15 mm/day of the norm. This high rainfall is likely caused by a triple effect of the normal monsoon rainy season, the ITCZ and the recent passage of the Madden-Julian Oscillation. Other suspected effects were the warm sea surface temperatures off the coast of Brazil and deforestation which caused climate change.





The above image shows rainfall measurements (inches) over South America for the past month and due to the lack of a detailed land-based network within the Amazon, few stations were found in the vicinity of the flooded regions.

Visitor Map
Create your own visitor map!

Updated: 12:40 GMT le 10 mai 2009

Permalink

Patterns in the ITCZ

By: Weather456, 12:34 GMT le 09 mai 2009

Along the African coast, there appears to be no wave-like feature at the moment but that might change as the GFS is forecasting a similar feature to earlier this weak to track across the continent but instead of weakening, emerges over the Eastern Atlantic. I will continue to monitor this situation.

The 12Z NAM and other models are hinting on a possible development of low pressure area along the US East Coast next week (below). This development occurs near the Gulf Stream which is responsible for the genesis of Andrea in this vicinity in 2007. Another contributing factor to Andrea, which is absent in this case, is a surface-500 mb blocking ridge. In addition, isotherms (lines of equal temperature) cross the isobars (lines of equal pressure) indicating this feature lies within a frontal zone. Another important factor is that the gale force winds associated with this feature are not near the low pressure centre which further suggests a non tropical entity. There are hints of subtropical characteristics such as the organize cloud and rain fields are well enough organize for an extratropical storm and there is small window of low wind shear.

I can say it appears certain that a feature will develop along the US east coast but whether or not this feature will be non-tropical or subtropical is uncertain.

This feature is forecast to move toward the north and east, out to sea.

Elsewhere, the tropical Atlantic remains quiet and none of the models are forecasting development within the next 7 days.



Investigating patterns in the ITCZ

The Intertropical Convergence Zone (ITCZ), also called the Intertropical front, monsoon trough, equatorial heat trough or simply the equatorial trough is climatological trough of low pressure that straddles the equator where surface trades/winds from opposite hemispheres converge and rise to form a zone of increase cloudiness, convection and precipitation. Below I will discuss patterns within the ITCZ using a 30-day average rainfall chart from the Tropical Rainfall Measuring Mission (TRMM).

Average Structure

The TRMM image below indicates that the ITCZ roughly parallels the equator with varying magnitude and latitudinal extent.

The ITCZ is more diffuse and weakest over the Western Indian Ocean due to the coastal upwelling that occurs there off the Somalian coast.

The ITCZ has considerable extent across Eastern Indian Ocean, Indonesia and the Western Pacific and this is due to the monsoon and the Western Pacific Warm Pool.

Over the South American and African continents, the mean rainfall distribution has considerable larger latitudinal extent and tends to lie directly over the equator; this is due to various factors, including evapo-transpiration from vegetation.

There are two notable zonal asymmetries in the ITCZ. The first is the southeast extension of the ITCZ over the southwest Pacific referred to as the South Pacific Convergence Zone (SPCZ) and the “double” ITCZ in the Eastern and Central Pacific due to the effects of La Nina (see below).

The ITCZ and ENSO

There are interannual fluctuations within the ITCZ due the effects of El Nino and La Nina episodes. In the former, sea surface temperatures (SSTs) in the central and eastern become anomalously warm while in the latter the opposite occurs. In El Nino years, the two convergence zones on opposite hemispheres merge into one single zone near the equator. In La Nina years, the dry equatorial zone is forced to become drier due to the westward extend of cooler waters from the eastern Pacific. This forms a “double ITCZ that stretches even further west than normal.

Later this month, I will present more detailed information about the ITCZ, such as intra-seasonal variations, cyclogenesis patterns of the ITCZ, relationship with SSTs, etc.



Visitor Map
Create your own visitor map!

Updated: 16:38 GMT le 09 mai 2009

Permalink

Atlantic Basin Calms Down Convective-wise

By: Weather456, 10:31 GMT le 08 mai 2009

There is not much to speak of across the basin, except for a few showers offshore the US east coast which is associated with a speed convergence and a surface trough moving across the Bahamas and Cuba.

Additional showers are found along Jamaica, Hispaniola, Puerto Rico and the SW Atlantic between 70-55W, south of 25N.

Clusters of thunderstorms ate found along Central America; the Eastern Pacific and Northern South America, in association with the ITCZ.

The 06Z GFS is actually forecasting development along the South American coast on Sunday and because the extreme southwest Caribbean is favorable, I would monitor the area and look for any model consensus or consistency.

Satellite imagery this morning along with surface observations over the continent revealed a broad area of low pressure spinning right along the coast of Africa with clusters of convection north and south of the low’s centre. The available data continues to suggest a wave-like feature but with a weakening signature and the westward propagation of deep convection has cease as the cloud patterns become masked in the ITCZ. This feature remains one of the first signs of African Easterly Wave development due to its genesis, propagation and nature.

There are no other areas over the African continent of interest.





Visitor Map
Create your own visitor map!

Updated: 10:37 GMT le 08 mai 2009

Permalink

Tropical Update/Best Job In the World/Hurricane Humor

By: Weather456, 10:56 GMT le 07 mai 2009

Tropical Update

A cold front is moving across the Southeastern United States producing showers along and within 300 nm east of the boundary.

Meanwhile, a surface trough extending from the Caribbean over the SW Atlantic Ocean continues to produce scattered showers and possible thunderstorms over Hispaniola, Puerto Rico and the Leeward Islands. Due to this moisture surge, there was a flash flood risk for the island last night and this risk continues today but should diminish over the next 48 hrs as the trough shifts northwest and weaken under a building ridge.

Isolated showers are found along Central America and Northeast South America but no organize clusters to speak of.

Overall, vertical shear of the Caribbean and Gulf remains lower than normal for this time of year and instability across the region is near normal.

The tropical Atlantic remains hostile for any tropical development with strong westerly winds aloft superimposing dry stable air in the mid-low levels due to a later of Saharan Dust. While vertical wind shear is near the climatological norm, the tropical Atlantic remains more stable than normal for this time of year.

This morning’s satellite imagery continues to support a wave-like feature along the African coast near 8W south of 10N moving west near 10 knots. Satellite imagery revealed some rotation along the axis with clusters of deep convection to its north and south. There is a great amount of vorticity being generated along this feature and there are twin convergence areas north and south of the axis which is critical feature of tropical waves over the continent. This wave is expected to exit the coast through out the day and I’m waiting to see if this feature will be classified by the Tropical Prediction Center. However, I am not expecting tropical cyclone development from this feature.





Best Job in the World

BRISBANE, Australia, May 6 (UPI) -- Australian tourism authorities said a British man has been chosen for "the best job in the world," a caretaker position on a Great Barrier Reef island.

Tourism Queensland said Ben Southall, 34, of Hampshire, England, was chosen from a pool of 34,000 applicants from around the world for the six-month, $106,000 position as caretaker of Hamilton Island, The Times of London reported Wednesday.

Southall's duties will include updating a weekly blog as well as video and photo diaries with details of the fishing hiking, sailing, snorkeling and exploring he performs while on the island, Tourism Queensland said.

Tourism officials call the caretaker position "the best job in the world."

The new hire, who said he has never before visited Australia, is being lodged in a three-bedroom villa on the island.

"It's amazing," Southall said. "You think of a three- or four bedroom-house in England and it has nice red bricks and is quite small but this house is a dream, it's enormous and looks out over the Coral Sea and at least four or five people can stay at any one time."

Top Ten Reasons Why Hurricanes are like the Christmas Season

10. Decorating the house (boarding up windows).
9. Dragging out boxes that haven't been used since last season (camping gear, flashlights).
8. Last minute shopping in crowded stores.
7. Regular TV shows pre-empted for "specials".
6. Family coming to stay with you.
5. Family and friends from out-of-state calling.
4. Buying food you don't normally buy ... and in large quantities.
3. Days off from work.
2. Candles.

1 And the number one reason Hurricane Season is like Christmas...At some point you know you're going to have a tree in your house!

Hurricanes are very powerfull systems that do cause many deaths and damages yearly around the world and should be taken seriously.

Visitor Map
Create your own visitor map!

Updated: 21:28 GMT le 07 mai 2009

Permalink

Tropical Update

By: Weather456, 10:57 GMT le 06 mai 2009

Tropical Weather Summary

A broad upper ridge over the Eastern Pacific continues to support anticyclonic winds aloft which is helping to fuel thunderstorms over Central America with debris moisture spreading into the Western Caribbean. Broad trough of low pressure over the eastern Caribbean extending north across the SW Atlantic continues to interact with these winds aloft to produce scattered showers over the central and northern Lesser Antilles, Puerto Rico and the SW Atlantic to 30N, west of 70W. Breezy conditions are also being experienced here due to the pressure gradient between the subtropical ridge over the Atlantic and trough. This moisture will continue to produce scattered isolated showers over the Leewards and Puerto Rico today then shift west over Hispaniola, Eastern Cuba and Jamaica over the next 48 hrs.

The tropical Atlantic remains under a very stable airmass, with a good amount of Saharan Dust over the area.

An unofficial African Easterly Wave is now along 3W from 10N to 3N moving west near 10 knots based on satellite imagery and numerical model with strong convection along the African coast from 10W to the prime meridian. Another interesting feature is further west near 12W which may possible another wave-like feature but lacks any clear signature.





Visitor Map
Create your own visitor map!

Permalink

Tropical Update

By: Weather456, 10:37 GMT le 05 mai 2009

Clusters of thundershowers are found along Central America and the Yucatan Peninsula, caused by a broad area of low pressure enhanced by diffluent flow aloft on the eastern flank of upper ridge over South America.

Convection along the intertropical front (ITCZ) has died down and become diffuse and scattered.

A surface trough over the Eastern Caribbean continues to interact with diffluent flow aloft generating scattered showers and thunderstorms across the Islands. Last night, here in Saint Kitts thunderstorms rolled through around 10 pm and we received a total of 10.5 mm of rain. Radar imagery this morning continues to show showers and possible thunderstorms across the islands. This will gradually pull north and west over the Virgin Islands and Puerto Rico over the next 24 hrs.

This activity is also tied to the mid-upper level low just north of Haiti that continues to produce showers over the SW Atlantic. The surface trough over the Caribbean will be monitored incase it tries to be convectively active once in the Western Caribbean.

Two features along an active ITCZ across West Africa continues to be monitored for tropical wave development. The first area (A) may possible be a tropical wave. The other area further east (B) is more convectively active. There is some wind shift/vorticity seen at 500 mb-700 mb where AEWs are normally found and the westward propagation is evident. At the moment, neither has enough evidence for a 100% confirmation. I will continue to monitor these areas.





Afternoon Update

Recent information regarding the 700 atmosphere showed that the feature over African (area B) appears to an African Easterly Wave. The TPC has not confirmed it but I work independent of the TPC so I'll refer to it as a unofficial African Wave.

The wave has become more evident on satellite imagery and 500 mb vorticity has increase along this feature. There are wind shifts and PV maxima along the axis and these are the features I look for most when confirming a tropical wave. Most of the available data supports an African Easterly Wave.



Visitor Map
Create your own visitor map!

Updated: 18:01 GMT le 05 mai 2009

Permalink

Surface Troughs Everywehere

By: Weather456, 11:24 GMT le 04 mai 2009

Overall, the Atlantic is quiet with a few surface troughs helping to generate some showers across the basin.

A frontal system is tracking across Southern United States while generating strong thunderstorms and showers from Louisiana to Georgia. Scattered showers found elsewhere between 95W and 80W, north of 27N.

Broad area of thundershowers across the equatorial Pacific, Caribbean and Northern South America are associated with ITCZ and NECZ.

Anticyclonic upper winds emanating from these thunderstorms are enhancing scattered showers across the Caribbean basin north of 12N. In addition, these winds are interacting with a surface trough near 65W to help maintain additional scattered showers across the Leeward Islands. We picked up about 6.4 mm of rain last night here in Saint Kitts. This surface trough will be monitored as it track west incase it tries to become convectively active.

Mid-upper level circulation, northeast of the Bahamas continues to interact with a surface trough to help produce scattered showers between 70-60W, north of 25N with the tail end of the system extending southwest to Leeward Islands. The area remains an open trough and though vertical wind shear is forecast to relax some, the area is forecast to be absorbed into the advancing frontal system over the SE USA, and thus will not have time to aquire a surface low and subtropical characteristics.

There is another area in the Subtropical Atlantic associated with a broad trough of low pressure. No development expected.

Over in the east, showers and thunderstorms extend along the ITCZ across the Atlantic and Gulf of Guinea with rotation seen near 0W. I will continue to monitor an area of tropical wave (not tropical cyclone) development.

The 6Z GFS is forecasting the development of a low pressure area along the Colombian coast next Monday. While this is in the more reliable time frame of 168 hrs, I cannot put much faith in it until I see consistency within that time frame and model consensus. Otherwise, there are no other areas of concern.



Tropical Storm Dante

Tropical Storm Dante left at least 20 dead, 3 missing and thousands displayed as the storm swirled over Mindoro Island south of Luzon before blowing out into the South China Sea on 2 May.

But as it was leaving, a low pressure area, gained strength and blew in from the Philippine Sea, hitting the eastern-most island of Catanduanes.

As of 4 May, 15 people were confirmed buried in landslides in the provinces of Barangay Hubo, Magallanes, and Sorsogon. Others died from electrocution and drowning.

The Department of Social Welfare and Development (DSDW) reported that as of 4 p.m., May 3, a total of 55, 346 persons or 9, 676 families had been evacuated to 165 evacuation centers in Bicol due to the floods and heavy rains.


Figure 1. TRMM satellite-based rainfall (mm) accumulations for 1 week.


Figure 2. Tropical storm Kujira batters central Philippines

Visitor Map
Create your own visitor map!

Updated: 13:47 GMT le 04 mai 2009

Permalink

Understanding the Atlantic Hurricane Season: Vertical Wind Shear

By: Weather456, 10:13 GMT le 03 mai 2009

Tropical Update

There aren’t any areas of interest in the Atlantic basin itself and none of the models are forecasting development within the next week. The ITCZ across the Tropical Atlantic and Eastern Pacific have been quite active over the past day or two due to the onset of the MJO but nothing that seems to be brewing yet.

A surface trough northeast the islands will eventually move west and be absorbed into an advancing frontal trough.

A non-tropical low in the North Atlantic is expected to dissipate.

There is a feature that I’m monitoring over the African continent that has mid-level vorticity maxima. It does not quite fit the criteria of an African Easterly wave but the reason I’m watching it is because the GFS is forecasting the emergence of a tropical wave feature this week.



Understanding the Atlantic Hurricane Season: Vertical Wind Shear

What is vertical wind shear?

Vertical wind shear is defined as the change in wind speed or direction with height, that is, between the 850 mb and 200 mb levels and in some cases the 600 mb and 200 mb levels (mid-level shear).

Why is wind shear not conducive for tropical development?

Tropical cyclone development and intensity is maintained by a vertical column of warm air near the center called a warm-core. This develops from the release of latent heat within thunderstorms. In an ideal tropical cyclone, warm moist air rises or is elevated within these warm columns and maintains the development of thunderstorms and consequently the tropical cyclone.

Vertical shear however, disrupts this mechanism by redistributing the warm column much like a cold wind blowing against expose skin (wind chill). Wind shear also causes the tropical cyclone to become vertically tilted causing the beneficial inflow and updraft to travel a longer distance to the condensation level.

What causes wind shear?

I like to group the causes of wind shear within two categories; the intraseasonal factors and the interannual factors.

Intraseasonal Causes

Troughs in the mid-latitude upper westerlies
The Tropical Upper Tropospheric Trough or TUTT
The African Easterly Jet (AEJ) – beneficial for tropical wave formation and maintenance

Interannual Causes

The El-Nino Southern Oscillation (ENSO)/Subtropical Jet

During El Nino, high SST over the eastern Pacific causes more deep convection there. The resultant outflow aloft enhances westerly wind shear over the Caribbean and western equatorial Atlantic. Consequently, the 200 mb anticyclonic flow necessary for tropical cyclones to develop is reduced. Normally in El Nino years the subtropical jet is further south.

Is it true that easterly wind shear is more beneficial to a tropical cyclone than westerly wind shear?

All wind shear is bad for tropical cyclones but a tropical cyclone will last longer under 20 knots of easterly shear as oppose to 20 knots westerly shear.

It is a very simple reason – in the Northern Hemisphere tropics the average surface wind direction is easterly, and if this is superimposed by easterly winds at 200 mb it would not have the same effect as westerly winds at 200 mb superimpose over the same surface easterly winds. The change in wind with height is greater with westerly shear than easterly shear in the deep tropics.

Can modest vertical wind shear be beneficial to a tropical cyclone?

Some tropical systems under 15-20 knots of shear can strengthen faster than those under 0-15 knots of shear but the overall intensity will be much lower. This is due to baroclinic forcing within the tropical cyclone. An example would be the burst of convection that Tropical Storm Alberto displayed in June 2006.

Are there any other effects of vertical wind shear besides those discussed above?

Vertical shear present within the African Easterly Jet is a result of the temperature, moisture and dust gradient across West Africa. Southwesterlies blow from the Gulf Guinea across Sub-Saharan Africa, where it converges and rises within the ITCZ. The air is eventually expelled aloft and due to the Coriolis force is oriented towards the west forming the African Easterly Jet. Instability within the jet causes African Easterly Waves, which disrupts the circulation along West Africa and causes the dust outbreaks, we know as SAL.

Vertical wind shear present on the equatorward side of an advancing upper trough causes the onset of extratropical transition of tropical cyclones.

What is the wind shear forecast for the 2009 Hurricane Season?

There are two indicators I tend to look at to forecast the wind shear for the upcoming season:

ENSO - which is expected to be neutral and thus allowing near average wind shear.

TUTT - this feature is maintained by the subsidence within the subtropical surface ridge. The stronger the surface ridge, the deeper the TUTT and the stronger the associated wind shear. Because the subtropical ridge is expected be stronger than normal this year, implies stronger shear associated with the TUTT. A good example was the hurricane season of 2007. While 2007 was a La Nina year, many storms died in the Atlantic due to strong vertical shear not from ENSO but the TUTT itself. The two that manage, went south of the TUTT, Dean and Felix. However, the high this year will not be as anomalously strong as in 2007. This and other factors form the basis that mnany of this year's storm will form close to home.

Weather456

Understanding the Atlantic Hurricane Season: The SST Factor
Understanding the Atlantic Hurricane Season: Technical Terms
Tracking Tropical Cyclones Part 1: Center Fix
Tracking Tropical Waves


Figure 1. Depiction of favorable and unfavorable conditions for tropical cyclone development.


Figure 2. Conceptual model of the African Easterly Jet through 5W west. Correction: where it says 850 mb geopotential it should say 500 mb geopotential height.


Figure 3. A montage showing the main causes of vertical wind shear with TUTT axis and troughs in the upper level westerlies (purple), African Easterly Jet (yellow) and the El Nino Southern Oscillation/Subtropical Jet (red). Not based on current conditions.

Visitor Map
Create your own visitor map!

Updated: 13:38 GMT le 03 mai 2009

Permalink

Tropical Updates Begins

By: Weather456, 10:02 GMT le 01 mai 2009

Tropical Updates Begins

Well it’s May and the 2009 Hurricane Season commences in 1 month. I have worked around some issues and if the good Lord continues to give me the breath of life I will be here for the whole season and next year as I finish university and school life in July.

I often refer to May as the transition between spring and summer and when the conditions necessary for cyclogenesis begin to take shape and thus this is the time I begin to look at the tropics both in the Atlantic and as it affects the west coast of Central America. Last year I posted a blog that discussed the nature of the tropics in May and basically states May tropical cyclones are rare but they do form. The most recent example was Tropical Storm Arthur of last year and before that, Subtropical Storm Andrea in 2007.

There are numerous observed dates and upcoming periods in May. Firstly, the Eastern Pacific Hurricane Season commences on the 15, NOAA normally issues their first hurricane season outlook in May and hurricane preparedness week which is to be held May 24 through 30. I will issue my 2009 outlook on May 16.

May 1-15 Outlook

Currently there aren’t any areas of interest in the tropics but there is a high chance of above-average rainfall across the tropical eastern Pacific and Caribbean as a vigorous upward pulse of the MJO is expected to move into the region soon. During this time, the GFS/NOGAPS was hinting on potential tropical development either in the eastern Pacific and/or West Caribbean Sea next week. While this is not totally farfetched (since the conditions will be there) we still have incorporate climatology and reliability of long-range forecasts and then it becomes highly unlikely. The two models have since dropped it.

In addition, increase in tropical moisture will also be found in the east, that being, Sub-Saharan Africa and at this time, I expect that we may see our first tropical wave. There have been two weak disturbances that resemble tropical waves back on April 14 and April 28-30 but none have been confirmed due their very weak reflections.

Discussion

There is an area of showers across Central America and Mexico extending across the Northwest Caribbean to Cuba. This activity is being caused by an upper level low along that sits along the West coast of Mexico near the Gulf of Tehuantepec.

Scattered clusters of thunderstorms along Colombia and Panama caused by the instability associated with the Colombian Low in conjunction with the ITCZ.

Another broad area of showers northeast of the Islands being caused by a surface trough as it interacts with an advancing upper trough.

As for the far east, a dry stable airmass associated with the Saharan Air Layer (SAL) sits over the tropical Atlantic, with stable air stratocumulus clouds beneath.

None of these areas poses to become anything of interest since vertical shear is high and the air is relatively dry and stable across the tropics.



Update

An area of showers northeast of the Leeward Islands is associated the diffluent flow east of a mid-upper low at 24N/56W enhanced at the lower levels by a highly amplified surface trough. This area remains enveloped within a broad area of dry air to its west and south. The area also remains in an extremely baroclinic environment with high vertical wind shear and low sea surface temperatures; neither of which is expected to become favourable for tropical development in the next 48 hrs. Thus any development, if any, will most likely be subtropical or non tropical in nature.



Weather456

Visitor Map
Create your own visitor map!



Updated: 23:38 GMT le 01 mai 2009

Permalink

About Weather456

With a Bachelors Degree in Environmental Sciences (2009), began tracking tropical storms in 2002 and is now a private forecaster.

Weather456's Recent Photos

Outflow boundary
African Dust
Surreal
Rainy Day