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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Thanks Storm.
SAB thinks this is at 10N still, that's why its so low.
Area of disturbed weather to the east of 91L looking strong this morning...
Link
Same thing that happened with Alex. Thats why its taking these storms so long to make depression status.
Good morning Aquak! I agree, paid is better.
Folks, the longer this thing takes to develop, the worse the outcome.
Yup. With TAFB at 2.5 and SAB at 2.0 91L should be upgraded to TD 4
The initiation point is very important.
You're right. I live in South Florida and most of the models, at the moment, are predicting a curve from our shores. But yesterday morning they were inching towards us. Let's see what the next batch of models say next.
Exactly. Neither am I miami. Its like everyone says, when the first runs come out 9 times out of 10 thats where the storm wont go lol. Im waiting for tropical depression status so the models have a center to lock on to. Till then I think the models are out to lunch.
Ok, are the same thing. But we have SAB at 2.0, and TAFB at 2.5. CIMSS ADT doesn't start until we have a named storm, it appears.
Good. Back to work for me too. Weekend went by too fast!
Looks like we're not getting a T.D. until 11 am EDT.
This thing is more organized than it's been. It looks like a depression. It looks better than Bonnie.
"Surface Circulation is Key"
Well, Maybe the problem with the storms developing could be the
Jinks 1 2 3 4 5 6 7
I like saying Morning when I get to agree with ya.. So "morning!"
Looks like TD 1 of last year
SAB, JK, VI, 5, 2020 /////, , , , LLCC, T, DT=2.0 BO CBND MET=2.5 PT=2.0 FTBO DT PA=50 NMI
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