From Jeff Masters - Weather Underground:
Potentially dangerous Lesser Antilles tropical disturbance 92L forms
A tropical disturbance (92L) has developed over the extreme southeastern Caribbean just north of the coast of South America, over the southernmost Lesser Antilles Islands. Surface observations indicate that pressures have been slowly falling at a number of stations, and satellite loops show a modest region of heavy thunderstorm activity is building. A strong flow of upper level easterly winds is creating a moderate 10 - 20 knots of wind shear, and the waters are plenty warm for development. Water vapor satellite loops show a large area of dry air lies over the northern Caribbean, but this dry air should not interfere with development over the next two days.
The disturbance is slowly drifting westward, but steering currents favor a more northwest motion Friday and Saturday. Lower shear lies over the Central Caribbean, away from the coast of South America, so any northward component of motion will allow for more significant development. There is drier air to the north, but 92L is steadily moistening the atmosphere in the Caribbean, so dry air may not be a problem for it. There is substantial model support for development. The disturbance is in a dangerous location for development, and gives me the greatest concern of any Atlantic disturbance so far this year. The models predict that by Saturday, 92L will bring heavy rains to Puerto Rico. These rains will then spread to the Dominican Republic on Sunday, and Haiti, Jamaica, and eastern Cuba on Monday. The longer range track of 92L is uncertain, and will strongly depend on where the storm drifts during the next two days. The ECMWF and GFS models predict a more southerly path through the Western Caribbean towards Belize and Mexico's Yucatan Peninsula, and the NOGAPS and Canadian models predict a more northerly path along the length of Cuba towards Florida. NHC is giving 92L a 40% chance of developing into a tropical depression by Saturday. Stay tuned.