Tropical Cyclone To Form Tonight or Tomorrow

The National Hurricane Center (NHC) has begun to issue advisories on Potential Tropical Cyclone 9, located 340 miles southeast of the Leeward Islands.Winds are near 40 mph, but the system lacks a well defined center and circulation needed to be called a tropical storm. 

However, it is expected to develop into Tropical Storm Isaias tonight or tomorrow before moving over the islands starting tomorrow afternoon. 

National Hurricane Center forecast cone for PTC #9

In their 5pm Discussion, the NHC said that "The overall structure of the disturbance has not changed much since this morning. New clusters of convection have developed over the northern portion of the elongated circulation and the Air Force Reserve reconnaissance aircraft has been unable to find a well-defined center."

"The global model guidance suggests that the system will consolidate overnight and should acquire a better defined center. As this occurs, the disturbance is likely to gradually strengthen within the low vertical wind shear environment that it is situated in." Wind shear is the difference in wind speed as you move up and down in the atmosphere. High shear inhibits development of cyclones, while low shear is favorable for development.

Depending on the exact track, this system could impact much of the Lesser Antilles, U.S. and British Virgin Islands, Puerto Rico, Hispaniola, and possibly even the Bahamas and Florida. It is expected that if it is stronger, it will move more northward, and if it is weaker, it will move westward.

Interaction with land could cause it to stay relatively weak. However, if it passes near, but not over, these islands, it could strengthen more.

Winds are occurring mainly to the northeast of the center.