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95L drenching the Keys, could develop into a tropical depression

By: Dr. Jeff Masters, 2:12 PM GMT on October 17, 2011

A large low pressure system centered about 100 miles north of Mexico's Yucatan peninsula, Invest 95L, is bringing heavy rains to Western Cuba and South Florida. Rainfall amounts in excess of 3 inches have been common across South Florida since Saturday; Miami has picked up 3.40" as of 10 am EDT this morning, and Key West Naval Air Facility recorded 9.72". Rains of 5 - 8 inches have fallen over much of the Florida Keys and Central Cuba since Sunday, according to radar rainfall estimates from the Key West Radar. Long-range radar out of Key West shows rain is affecting most of South Florida south of Fort Myers, but there is no obvious spin to the echoes, and no evidence of organized spiral bands forming. Satellite loops show that 95L has a respectable amount of heavy thunderstorm activity that is increasing in areal coverage. There is no evidence of a well-formed surface circulation trying to develop, though surface observations in the Western Caribbean do show that 95L has a broad counter-clockwise circulation. Two ships to the north of 95L's center measured sustained winds in excess of 30 mph this morning, but no land stations are reporting sustained winds over 30 mph. Water temperatures over the regions are near 29°C, which is plenty warm to support a tropical storm.

Figure 1. Morning satellite image of Invest 95L.

Figure 2. Predicted rainfall for the 5-day period ending 8 am Saturday October 22, 2011. Image credit: NOAA/HPC.

Wind shear over 95L is currently a moderate 10 - 20 knots, and is expected to stay in the moderate range through Tuesday night. NHC is giving the system a 60% chance of developing into a tropical depression by Wednesday, and has scheduled a hurricane hunter aircraft to investigate the system this afternoon at 2 pm EDT. The models are generally showing only weak development of 95L. The storm is currently moving north at 5 - 10 mph, but should turn to the northeast by Tuesday afternoon, as it gets caught up by an approaching trough of low pressure. This trough should pull 95L into the west coast of Florida on Tuesday night or Wednesday morning between Fort Myers and St. Marks. Portions of southwest Florida could receive up to 5 inches of rain from 95L; locations to the north of Tampa will less rain, due to the large amount of dry air over the northern Gulf of Mexico that will affect the northwestern portion of the storm. Once 95L meets up with the trough, wind shear will rise sharply, and it is unlikely 95L will be able to grow any stronger than a 50 mph tropical storm before landfall occurs. It is more likely that 95L will have top winds of 35 - 45 mph Tuesday night near the time of landfall.

Another area of disturbed weather in the Eastern Atlantic, 1400 miles east of the Lesser Antilles Islands, has developed a modest degree of spin, but has very limited heavy thunderstorm activity. NHC is giving this system a 10% chance of developing into a tropical depression by Wednesday.

Jeff Masters


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