Lesser Antilles may see a tropical storm late this week
A concentrated area of intense thunderstorms near 9N 36W, midway between Africa and the Lesser Antilles Islands, has become more organized this morning. NHC has labeled this system Invest 91L, and is giving it a 60% chance of developing into a tropical depression by 8am Tuesday. Wind shear is a moderate 10 - 20 knots, sea surface temperatures are at record highs, and the dust and dry air of the Saharan Air Layer (SAL) are far enough to the north of 91L to potentially allow further development. The main negatives for development are the current phase of the Madden-Julian Oscillation, which favors downward motion over the tropical Atlantic, and the fact that 91L is too close to the Equator to take much advantage of the Earth's spin to get spinning. Last night's ASCAT pass of the region did show a large region of westerly winds south of 91L, indicating that a surface circulation is trying to form. Satellite imagery shows that the intensity and areal extent of 91L's heavy thunderstorms is increasing. However, there are no signs of a surface circulation, and low-level spiral bands and upper-level outflow are not apparent yet.
Forecast for 91L
There is strong model support for 91L developing into a tropical depression. The GFS, ECMWF, NOGAPS, and UKMET models all develop 91L into a tropical depression by Tuesday or Wednesday. A west to west-northwest motion is predicted, and residents of the Lesser Antilles Islands should anticipate the possibility of a tropical storm arriving in the islands as early as Thursday. It is possible that 91L would pass northeast of the islands, as predicted by the UKMET model, and it is too early to speculate on which of the islands is at most risk. As the storm approaches the Lesser Antilles late this week, 91L will encounter a strong upper-level low pressure system centered north of Puerto Rico. This upper-level low will likely bring high levels of wind shear to the waters just north of Puerto Rico and Hispaniola. Thus, if 91L stays to the south, in the Caribbean, it is far more likely to attain hurricane status than if it pushes north of the Caribbean. As always, long range forecasts of this sort are speculative, and it is too early to reliably say what the long-term risks of 91L becoming a hurricane are. The latest intensity forecast from the SHIPS model shows 91L peaking in strength four days from now, then weakening as it encounters the high wind shear area north of Puerto Rico.
Figure 1. Morning satellite image of Invest 91L.
Next update
I'll have an update Monday morning.
Jeff Masters
Reader Comments
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i 2nd that
Yeah, I did notice something of a vertical tilt from 850 to 500 mb.
NMFC Norfolk Tropical Feed
No Active Tropical Warnings in the Atlantic, Caribbean, or Gulf of Mexico
By Maritime.CDO@navy.mil (NMFC CDO) from Naval Maritime Forecast Center Norfolk Virginia. Published on .
As of Mon 02 Aug 2010 01:00:02Z
2010 Storms
All Active Year
Atlantic
91L.INVEST
East Pacific
NONE
Central Pacific
92C.INVEST(T.C.F.A.)
West Pacific
96W.INVEST
Indian Ocean
NONE
Southern Hemisphere
NONE
i see a white there so i assume that means it is strengthening???
Good to see the models going fishward at the moment, but I really don't put much into them until they have proper initialization fixes.
yes
Swiping the East Coast, close call recurvature. Or missing the trough as a ridge builds to the north, classic situation that happened with both Frances in 2004 and Alex of this year, stalls a bit until the ridge steers it towards the Southeast Coast. I just don't see a recurvature this this one.
same here
You could draw a couple similarities but Alex developed in a different way and in a different pattern. It's not the same thing here.
Invest91
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)
Dynamic Models (More sophisticated models)
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18z Early Cycle NHC model tracks
Invest91
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)
Dynamic Models (More sophisticated models)
Link
Looks like a caterpillar........
Yes, I think the site is getting a virus.
LOL. Trust the HWRF to have the northern-most bias of all computer models.
Link
Nope, and I never expected it to. Through this weekend I expected only a couple degrees of progress westward, which I explained somewhere last week. After today, it should start accelerating WNW. It already is starting to move now actually.
i can't see that track happening
Prob of RI for 30 kt RI threshold= 20% is 2.5 times the sample mean( 8.1%)
Prob of RI for 35 kt RI threshold= 12% is 2.5 times the sample mean( 4.8%)
Prob of RI for 40 kt RI threshold= 7% is 2.0 times the sample mean( 3.4%)
Yes i just got one so i will see ya all later.
NMFC Norfolk Tropical Feed
No Active Tropical Warnings in the Atlantic, Caribbean, or Gulf of Mexico
By Maritime.CDO@navy.mil (NMFC CDO) from Naval Maritime Forecast Center Norfolk Virginia. Published on .
As of Mon 02 Aug 2010 01:15:01Z
2010 Storms
All Active Year
Atlantic
91L.INVEST (T.C.F.A.)
East Pacific
NONE
Central Pacific
92C.INVEST(T.C.F.A.)
West Pacific
96W.INVEST
Indian Ocean
NONE
Southern Hemisphere
NONE
I got a message too. Ugh I hate when this happens on this blog. Time for a computer scan
nop
fiscaster
Indeed. The center is near 10.41N and 37.10W.
Viewing: 2551 - 2601
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