Disorganized showers and thunderstorms have developed near the Bahamas today. A surface trough is expected to form north of Puerto Rico early Thursday morning, and this system has a very small chance of acquiring subtropical or tropical characteristics by Saturday. Wind shear over the region is currently extremely high – about 70 knots. However, shear is likely to drop on Friday as an upper-level low will move into the region – giving this system a narrow window of tropical or subtropical cyclogenesis before the shear increases again by the weekend and the low moves into Florida.

North Atlantic 24-hour Shear Tendency. (Source: University of Wisconsin)

The 12z ECMWF, GFS and UKMET models all did not predict that this system would develop into a tropical or subtropical cyclone. However, less than half of the ensemble members predicted that some slight development was possible. The trough is expected to move westward to west-northwestward through the Bahamas on Friday, and into southeastern Florida on Saturday. The window for this system to acquire any subtropical or tropical characteristics appears to be very short, since the wind shear is only expected to be moderately favorable for a very short time on Friday.  Tropical cyclones are usually unable to develop central convection unless wind shear is approximately 20 knots or less, and that is likely to be a major issue with this system.

The National Hurricane Center (NHC) has not mentioned this system in a Special Tropical Weather Outlook, nor has the disturbance been given an “Invest” designation. I continue to give this system only a 10% chance of tropical or subtropical cyclone formation. In the unlikely event that this system becomes a tropical or subtropical cyclone with maximum sustained winds of at least 34 knots (39 mph), it would be named Alberto. The primary threat for this system will be heavy rains for the Bahamas and Greater Antilles.

I will be back with an update on this system by Friday.