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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i agree great outflow and a nice eye starting to form a bit thisisallin my blog
12z nam 72 hours out
Your info. and graphics are excellent P451...
Just My Opinion.
anyone else here care who was first to post something here???? not me.
According to Levi, that high pressure near Shreveport is supposed to move back to the west towards the Rockies.
It better get a move on.
Right, and I said it will take 12-24 hours to close off. Technically it can not be described as a LLC if it is not closed off. :) just being technical lol
Link
Click on Lat Lon square above loop.
Beautiful satellite image, that has the looks of an almost-hurricane, if not a hurricane.
What about a made-up acronym for MJO?
My Joking Opinion.
Thank you for saving me the trouble. :)
I just don't like people big noting themselves.
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 20 AUG 2011 Time : 134500 UTC
Lat : 16:28:10 N Lon : 87:14:32 W
CI# /Pressure/ Vmax
4.2 / 985.1mb/ 69.8kt
Final T# Adj T# Raw T#
4.2 4.3 4.3
Center Temp : -73.9C Cloud Region Temp : -71.8C
the dvorak intensity estimates all say its a cat.1 hurricane!
That's nothing new it always rains really bad in Central America, many places average 100 inches per year down there. Ive taken trips to Central America many times, they are always dealing with torrential rain causing mudslides, flooding and death.
I experienced unbelievably powerful thunderstorms there from just daytime heating.
So, its not like the rain from Harvey is anything new, but it certainly won't help. Its a tropical rainforest with lots of mountainous terrain, its gonna happen.
I agree, but I do believe it is already the strongest in the season (appearance wise).
Once the LLC closes off and it begins to BOOM, it is going to have a large wind field.
FWIW, I think any developing LLC is actually around 14 North (give and take a couple of tenths of latitude) and 54.5 West. This actually shows up quite well in RAMMB imagery
RAMMB visible loop of 97L
* By The Edge Restaurant
* Date: Sat, 20 Aug 2011 10:41:17 -0400
Looks like the tropical wave named invest 97L has its 1007 MB low centred right on St Lucias latitude about 350 miles to the the east of us. It just got very dark here, the winds picked up, it started to rain and I can hear the thunder getting closer. Looks like we are in for a wet day.
Annika
Bridge is severed, with a a bit weaker C CONUS High and with a departing E CONUS TROF keeping the path open long enough for 97L to gain some latitude.
LOL...in his defense, he is correct; the designation is his by unanimous decision. I abstained from the voting as I got in late
Cat. 1
We'll see. 50% hope so. 50% not. Break the Ts streak Harvey. You have 1 shot.
Hurricanes are not balanced at boundary layer levels. They bring in lots of air to the eyewall.
Developed hurricanes are balanced at mid levels and, sans a shear problem, do not ingest mid level air into the core.
From the COMET module here: http://www.meted.ucar.edu/tropical/textbook/ch10/ tropcyclone_10_2_1.html
(May require a free registration, if you haven't already.)
At the mid-levels, the winds are in a cyclostrophic balance between the pressure gradient and centripetal force. There is no inflow angle at mid levels. Thus, the hurricane will be insulated from some amount of dry air existing in the mid-levels (though vertical mixing into the boundary layer would be detrimental.)
Examples of mid-level wind balance are all over our observations, but here are a couple of examples.
(Hurricane Dean)
AMSU 700 mb; no inflow:
IR cloud drift, no inflow:
Full wind analysis: http://rammb.cira.colostate.edu/products/tc_realt ime/image_mpsatwnd.asp?storm_identifier=AL042007&p roduct_filename=2007AL04_MPSATWND_200708201800
Indeed the methodology for the creation of the "Multi-Platform Tropical Cyclone Surface Wind Analysis" states that it adds a "turn" to create an inflow angle when adjusting these mid-level sources of wind data to a surface wind field. Further, when any part of the wind field is over land, the friction slows the wind, requiring a further inflow angle due to being further out of cyclostrophic balance.
(These methods are NOT valid for anything but a well-developed TS, or stronger.)
Currently, this product combines information from five data sources to create a mid-level (near 700 hPa) wind analysis using a variational approach described in Knaff and DeMaria (2006). The resulting mid-level winds are then adjusted to the surface applying a very simple single column approach. Over the ocean an adjustment factor is applied, which is a function of radius from the center ranging from 0.9 to 0.7, and the winds are turned 20 degrees toward low pressure. Over land, the oceanic winds are reduced by an additional 20% and turned an additional 20 degrees toward low pressure.
http://rammb.cira.colostate.edu/products/tc_realt ime/about.asp#MPSATWND
If you have a lot of time on your hands, this document, The Structure and Energetics of the Tropical Cyclone is very, very good even though it is 35 years old. Very long (188 pages!), but easy to read and with little obfuscation.
http://raleighwx.americanwx.com/models/hwrf/00zhw rf500mbHGHTPMSLnest2hwrfLoop.html
97L is to take a turn south and west from Monday into Tuesday before returning to a west - northwest course.
Why? That is well within the 72 hours that we do have skill in predicting storm tracks. I do not see anything in that time frame that would cause 97L to do that.
What makes you say that? I mean, I'm someone who would much rather live in the country then this big city hustle and bustle, and yes people can be rude around here sometimes, but other than that its great.
You gotta learn to enjoy what you got, there is no such thing as paradise in this world, you just gotta appreciate what blessings you have, and learn to deal with the bad stuff.
So what do you dislike about this area so much?
Location: 16.8°N 87.6°W
Max sustained: 60 mph
Moving: W at 12 mph
Min pressure: 998 mb
10:00 AM CDT Sat Aug 20
Location: 16.8°N 87.6°W
Max sustained: 60 mph
Moving: W at 12 mph
Min pressure: 998 mb
Viewing: 4201 - 4251
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