A large area of disturbed weather – designated Invest 99L – has developed over the northwestern Caribbean Sea, Cuba, and the Florida Straits. This area of disturbed weather has moderate potential to develop into a weak tropical cyclone on Friday or Saturday. As of 00:00 UTC Friday, Invest 99L was centered near 24.2°N 79.9°W, and was moving slowly northward. Maximum sustained winds were 20 knots (25 mph), with an estimated minimum pressure of 1010 mb. On Friday, an area of low pressure is expected when the disturbance moves northward. Conditions are only marginally favorable for development, however.  During the next 36 hours or so, the disturbance will be over sea surface temperatures above 28°C (82.4°F), and wind shear will be light to moderate, at about 10-20 knots. 99L is expected to be in a moderately moist environment for the next 36 hours or so as well, with mid-level relative humidity values of about 60-65 percent. With the period of favorable conditions, there is a narrow window for 99L to become Tropical Depression Sixteen or Tropical Storm Nate by Sunday. On Sunday, shear is expected to increase quickly, while waters begin to cool. Development is unlikely after that time. Model support for 99L to develop is modest. The 18z Thursday GFS and ECMWF model runs showed very slight development of a low pressure area, while the 12z Thursday UKMET model run did not predict any development would occur. The National Hurricane Center (NHC) gives 99L a 40 percent chance of development within 48 hours, and a 50 percent chance within five days. While it seems very likely an area of low pressure will develop, it is uncertain if it will develop a sufficiently well-defined center and sufficient convective organization to be designated a tropical cyclone. The primary threat with 99L will be heavy rain in Eastern Florida and Georgia, and it is very unlikely that 99L will be a hurricane if it develops.

Meanwhile, Hurricane Lee is slowly weakening as it encounters strong shear and cooler waters, and Hurricane Maria has once again weakened back to a tropical storm. Lee is expected to become post-tropical and dissipate over the weekend. Maria is expected to also become a post-tropical cyclone on Saturday as it moves east-northeastward over the Northern Atlantic.

I will be back with another post tomorrow.