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97L still disorganized, but bringing heavy rains to the northeast Caribbean

By: Dr. Jeff Masters, 12:27 PM GMT on October 04, 2010

A large region of disturbed weather (Invest 97L) covers the Lesser Antilles Islands and waters near Puerto Rico and the Virgin Islands. The storm is headed west-northwest at about 10 mph, and will bring heavy rain showers and gusty winds to the Lesser Antilles, Puerto Rico, the Virgin Islands, and the Dominican Republic today. These showers can be seen on Martinique radar this morning, and Martinique reported a wind gust of 35 mph this morning during one of 97L's heavy squalls. An upper level trough of low pressure is contributing to the heavy rain showers by making the atmosphere more unstable. This same trough is also bringing moderate wind shear of 10 - 20 knots, which will keep any development today very slow to occur. Recent satellite imagery shows a large area of intense thunderstorms associated with 97L, but the activity is not well organized, and there are no signs of a surface circulation. Long range radar out of Puerto Rico also shows no signs of rotation.

Figure 1. Morning satellite image of Invest 97L.

Forecast for 97L
The SHIPS model predicts that wind shear over 97L will slowly fall over the next three days, reaching the low range, 5 - 10 knots, by Thursday, which may allow the storm to develop into a tropical depression, if its center can stay over water. All of the major computer models now show development of 97L into a tropical depression Wednesday or Thursday, just north of Hispaniola. By Thursday, a passing trough of low pressure is expected to pull 97L to the northeast away from Hispaniola, and rains should end by Friday on the island if this forecast verifies. NHC is giving 97L a 20% chance of developing into a tropical depression by Wednesday. 97L will move at about 5 - 10 mph today through Wednesday, bringing the potential for an extended 3-day period of heavy rains for the islands in its path. These rains may result in life-threatening flash flooding and mudslides in Puerto Rico and the Dominican Republic today through Wednesday, and for Haiti Tuesday through Thursday. Flash flood watches are posted for the Virgin Islands and Puerto Rico today.

Elsewhere in the tropics
An area of disturbed weather near 10N, 47W is under a high 20 knots of wind shear, and is headed northwest into a region of even higher wind shear of 20 - 30 knots. Satellite imagery shows only a limited amount of heavy thunderstorms, and there is plenty of dry air in the vicinity that is interfering with development. NHC is giving the disturbance a 10% chance of developing into a tropical depression by Wednesday.

Most of the models indicate the possibility that a strong tropical disturbance capable of becoming a tropical depression will form in the Central or Southern Caribbean 6 - 8 days from now.

Next update
I'll have an update Tuesday morning.

Jeff Masters


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