TD 8 forms; 97L a potential threat to the Caribbean and U.S.
Tropical Depression Eight formed last night near the coast of Honduras, and is headed westwards towards a landfall in Belize on Saturday. TD 8 is a small storm, so will impact a relatively small area of northern Honduras, northern Guatemala, all of Belize, and southern portions of Mexico's Yucatan Peninsula. TD 8 has just enough room between its center and the coast of Honduras to intensify into a moderate strength tropical storm with 50 - 60 mph winds before landfall. It is very unlikely TD8 has the time or room to intensify into a hurricane; NHC gave the storm just a 7% chance of making it to hurricane strength in their 11am EDT wind probability forecast. Should TD8 make it to tropical storm strength, it would be called Harvey.
Figure 1. Morning satellite image of TD 8.
Invest 97L likely to become a tropical storm next week, could threaten the U.S.
A tropical wave near 14°N 48°W, about 800 miles east of the Lesser Antilles Islands, is moving westward near 20 mph. This wave, designated Invest 97L by NHC yesterday, has seen a marked increase in its heavy thunderstorm activity this morning, but dry air to the north and west is slowing development. An impressive amount of large-scale spin is obvious in visible satellite loops, but the storm is at least a day away from forming a well-defined surface circulation. Ocean temperatures are about 28.5°C, about 2°C above the threshold needed to support a tropical storm, and wind shear is low, 5 - 10 knots.
Figure 2. Morning satellite image of the tropical wave 97L.
The computer models have shown an unusual amount of agreement in developing 97L over the past few days, and all the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C. The main impediment for development will likely be two-fold: too much dry, stable air, and proximity to land.
As seen in Figure 3, there has been an unusual amount of dry, stable air in the Atlantic this year, due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. This stable air has been largely responsible for the fact that none of our seven tropical storms so far this year has made it to hurricane strength, despite the presence of sea surface temperatures that are the 3rd warmest on record across the tropical Atlantic. Tropical Storm Emily in early August encountered problems with dry air when it crossed the Northeast Caribbean, and 97L may have similar difficulties.
Figure 3. Vertical instability of the atmosphere during 2011 in the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Observed vertical instability (blue line) has been much lower than the climatological average from previous years (black line), due to an unusual amount of dry air in the atmosphere, inhibiting tropical storm development this year. Image credit: NOAA/CIRA.
Encounters with land will be another potential major problem for 97L. Most of the computer models take 97L near or over Puerto Rico Sunday night, then very close to or over mountainous Hispaniola Monday night through Tuesday. It is unlikely that 97L will be stronger than a 55 mph tropical storm when it encounters these islands, and passage over the islands could severely disrupt the storm. However, if 97L takes a path just south or north of Hispaniola, the potential exists for the storm to intensify into a hurricane.
There will be moderate wind shear of 10 - 20 knots to the north of the islands early next week, so a path just to the south of the Dominican Republic and Haiti would be more likely to let 97L intensify into a hurricane. A west-northwest motion is likely for 97L through Wednesday, which would bring the storm to the vicinity of Jamaica-Central Cuba-the Central Bahamas on Wednesday. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn 97L to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when 97L will turn to the north. The best model for predicting the timing and strength of such troughs over the past two years has been the ECMWF (European Center model), and this model currently brings 97L into the Florida Keys on Thursday night next week. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models.
Remember that a 7-day forecast by even our best model will be off by an average of over 700 miles, so it is too early to tell what part of the U.S. might be most at risk from a strike by 97L. This weekend would be a good time to go over your hurricane preparedness.
Figure 4. Morning satellite image of Invest 98L off the coast of Africa.
Invest 98L near the coast of Africa
A tropical wave near the coast of Africa, a few hundred miles southeast of the Cape Verde Islands, is moving west to west-northwestward at 10 - 15 mph. This wave, designated Invest 98L by NHC yesterday, is large and well-organized, with a modest amount of spin and heavy thunderstorm activity. 98L will bring strong, gusty winds and heavy rains to the Cape Verde Islands today and Saturday as the storm skirts to the south. So far this morning, top sustained winds measured in the islands were 24 mph at Mindelo. Water temperatures are warm, near 27 - 28°C, and wind shear is low, 5 - 10 knots, so 98L should continue to organize today. NHC gave the storm a 50% chance of developing into a tropical depression in their 8am advisory. Once 98L passes to the west of the Cape Verde Islands, it has a long stretch of ocean to cross before it could affect any other land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, but it is too early to be confident of this.
Jeff Masters
Reader Comments
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Well, it isn't going to have a nice eyewall and eye with deep convection, at least not right now.
It is impressive considering its environment.
Systems near Africa sure is active though.
I've been puzzled by all the comments that 97L is looking 'healthy'. All I see is just a fuzzy blob with no banding, just like we've seen all season with the other invests. It'll still be a fuzzy blob by the time it gets into the Carib, just like Don, Emily et al. Wouldn't be surprised if it never makes it past TD status, like all the rest of them.
It looks good to me. Maybe it is hurt just slightly by the dry air.
Definitely. The chances of this becoming a hurricane are increasing.
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 19 AUG 2011 Time : 194500 UTC
Lat : 16:12:33 N Lon : 84:22:23 W
CI# /Pressure/ Vmax
3.4 / 995.5mb/ 53.0kt
Final T# Adj T# Raw T#
3.4 3.5 3.9
11081918EP9111_ships.txt 19-Aug-2011 19:54 5.6K
11081918AL9811_ships.txt 19-Aug-2011 19:20 5.8K
11081918AL9711_ships.txt 19-Aug-2011 19:11 6.1K
11081918EP0711_ships.txt 19-Aug-2011 19:08 5.6K
11081918AL0811_ships.txt 19-Aug-2011 19:08 6.1K
11081918EP0611_ships.txt 19-Aug-2011 19:01 5.6K
7 active areas, can only run hurricane models (HWRF & GFDL) on 5, so 2 will be odd men out.
Looks like 97L will miss you.
And the problem with that, is...???
Well then it is you against most (I think) other highly skilled forecasters who predicts this thing to become a hurricane.
Please elaborate on your opinion. Is it based on anything other than a hunch?
LOL.. Yeah, it's in its developing stages and people want to say it looks sick. Take a look at what it looked like yesterday compared to today then get back to me. Parched my but
BULLETIN
TROPICAL STORM HARVEY ADVISORY NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL AL082011
500 PM EDT FRI AUG 19 2011
...HARVEY STRENGTHENING AS IT APPROACHES THE BAY ISLANDS...
SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...16.5N 84.7W
ABOUT 125 MI...205 KM E OF ISLA ROATAN HONDURAS
ABOUT 240 MI...390 KM ESE OF BELIZE CITY
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES
NWS NATIONAL HURRICANE CENTER MIAMI FL AL082011
500 PM EDT FRI AUG 19 2011
EARLIER REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
INDICATED THAT TROPICAL DEPRESSION EIGHT WAS ON THE VERGE OF
BECOMING A TROPICAL STORM. SINCE THAT TIME...THE CONVECTIVE
BANDING HAS BECOME MORE PRONOUNCED AND SATELLITE ESTIMATES FROM SAB
AND TAFB HAVE INCREASED TO 45 KT. BASED ON THESE DATA...THE
DEPRESSION WAS UPGRADED TO TROPICAL STORM HARVEY AT 1800 UTC AND IS
NOW ESTIMATED TO HAVE WINDS OF 40 KT. THE NEXT AIRCRAFT IS
SCHEDULED TO REACH THE STORM NEAR 00Z.
THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 280/10. THERE IS NO
CHANGE IN THE SYNOPTIC REASONING FOR THE TRACK FORECAST. A
LOW/MID-LEVEL RIDGE OVER THE GULF OF MEXICO AND THE NORTHERN GULF
COAST IS EXPECTED TO GRADUALLY STRENGTHEN DURING THE NEXT 48-72
HOURS...AND THIS SHOULD STEER THE CYCLONE GENERALLY WESTWARD TO
WEST- NORTHWESTWARD THROUGH ITS LIFETIME. ONE CHANGE SINCE THE LAST
ADVISORY IS THAT THE GUIDANCE ENVELOPE AND THE FORECAST TRACK HAVE
SHIFTED A LITTLE TO THE NORTH...BRINGING THE CENTER BRIEFLY OVER
THE BAY OF CAMPECHE BETWEEN 48-72 HOURS. THE NEW FORECAST TRACK IS
IN THE CENTER OF THE GUIDANCE ENVELOPE NEAR THE VARIOUS CONSENSUS
MODELS.
CURRENT CONVECTIVE TRENDS AND GOOD CIRRUS OUTFLOW IN THE
NORTHWESTERN SEMICIRCLE SUGGEST HARVEY SHOULD CONTINUE TO
STRENGTHEN UNTIL LANDFALL IN BELIZE. THE NEW INTENSITY FORECAST
CALLS FOR A PEAK INTENSITY OF 55 KT NEAR LANDFALL IN BEST AGREEMENT
WITH THE SHIPS AND LGEM MODELS. THEREAFTER...HARVEY SHOULD SLOWLY
WEAKEN AND EVENTUALLY DISSIPATE OVER SOUTHEASTERN MEXICO. THERE
ARE TWO NOTES ABOUT THE INTENSITY FORECAST. FIRST...THE RAPID
INTENSIFICATION INDEX OF THE SHIPS MODEL SHOWS A 40 PERCENT CHANCE
OF 25 KT OF INTENSIFICATION DURING THE NEXT 24 HOURS...AND THE
INTENSITY PROBABILITIES TABLE SHOWS A 13 PERCENT CHANCE OF HARVEY
BEING A HURRICANE IN 24 HOURS. SECOND...THE INTENSITIES LATER IN
THE FORECAST PERIOD COULD REQUIRE ADJUSTMENT IF THE CENTER MOVES
FARTHER OUT INTO THE BAY OF CAMPECHE THAN CURRENTLY FORECAST.
FORECAST POSITIONS AND MAX WINDS
INIT 19/2100Z 16.5N 84.7W 40 KT 45 MPH
12H 20/0600Z 16.7N 86.1W 45 KT 50 MPH
24H 20/1800Z 17.1N 87.9W 55 KT 65 MPH
36H 21/0600Z 17.6N 89.9W 40 KT 45 MPH...INLAND
48H 21/1800Z 18.0N 91.9W 30 KT 35 MPH...INLAND
72H 22/1800Z 18.5N 96.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 23/1800Z...DISSIPATED
$$
FORECASTER BEVEN
Certainly an uptick in the intensity forecast.
INTENSIFICATION INDEX OF THE SHIPS MODEL SHOWS A 40 PERCENT CHANCE
OF 25 KT OF INTENSIFICATION DURING THE NEXT 24 HOURS.
Considering where it is at currently its no surprise. It really won't look any better than it currently is till it passes 50W, where there is less dry air and ALOT warmer water temperatures to support more convective activity. Once it can get more convection over its center as time goes on it can mix out a lot of the dry air that has been intruding on it.
Ya, they discussed whether it would be strong enough to cause the system to go north or weak and the system continues westward. Uncertainty remained high.
I have been Conversin' with the Jumbies and stuff.
They promised me a Bright and Cheery day tomorrow.
But they did say "look out for middle/late of next week" so I am Prepared!
Tropical Cyclone Advisory #13
TROPICAL CYCLONE GREG (EP072011)
2:00 PM PDT August 19 2011
=====================================
SUBJECT: GREG Continues To Weaken Over Cooler Waters
At 18:00 PM UTC, Tropical Storm Greg (994 hPa) located at 19.6N 117.0W or 445 NM west southwest of southern tip of Baja California, Mexico has sustained winds of 50 knots with gusts of 60 knots. The cyclone is reported as moving west at 10 knots
Dvorak Intensity: T3.0
Gale Force Winds
===============
70 NM from the center
Forecast and Intensity
======================
24 HRS: 19.7N 120.5W - 35 knots (Tropical Cyclone)
48 HRS: 19.3N 123.7W - 25 knots (Tropical Depression)
97L looks healthier today.
It's based on what we've seen so far this season. Fuzzy blobs with no banding, that fizzle out well short of hurricane status.
Development has been suppressed by subsiding air and dry air throughout the region. Any reason to think that's going to change soon?
No, there is no reason to think that we should start seeing hurricanes soon.
I agree 100%.
Don't get off work until 5:30...:/
Hanging with the crowd
Putting your business in the street talking out loud
Saying you bought her this and that
And how much you done spent
I swear she must believe it's all heaven sent"
It is what it is.
Tropical Cyclone Advisory #17
TROPICAL DEPRESSION, FORMER FERNANDA (EP062011)
11:00 AM HST August 19 2011
=====================================
SUBJECT: FERNANDA Weakens Into A Tropical Depression
At 18:00 PM UTC, Tropical Depression, Former Fernanda (1005 hPa) located at 15.4N 145.8W or 610 NM east southeast of South Point, Hawaii has sustained winds of 30 knots with gusts of 40 knots. The cyclone is reported as moving west at 10 knots
Dvorak Intensity: T2.0
Forecast and Intensity
======================
24 HRS: 16.0N 149.3W - 25 knots (Tropical Depression)
Viewing: 1251 - 1301
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