Tropical Storm Warnings Issued for Northwestern Bahamas

The government of the Bahamas issued Tropical Storm Warnings for the Northwestern Bahamas on Friday afternoon.  Tropical Storm Warnings were issued for the Abacos, Berry Islands, Bimini, Eleuthera, Grand Bahama Island and New Providence.  A tropical disturbance over the Southeastern Bahamas was forecast to strengthen into a tropical storm, which prompted the issuance of the Tropical Storm Warnings.  The National Hurricane Center (NHC) initiated advisories on the disturbance at 5:00 p.m. EDT on Thursday and NHC designated the system at Potential Tropical Cyclone Nine.

At 5:00 p.m. EDT on Thursday the broad center of Potential Tropical Cyclone Nine was located at latitude 23.7°N and longitude 74.8°W which put it about 235 miles (380 km) southeast of Great Abaco.  It was moving toward the northwest at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1008 mb.

The circulation around Potential Tropical Cyclone Nine was very poorly organized.  There was a very broad center around which the air was turning cyclonically.  An Air Force Reserve Hurricane Hunter reconnaissance plane was finding weak winds near the broad center.  Most of the strong thunderstorms were northeast of the broad center of the disturbance.  The stronger winds here occurring near those thunderstorms.  There did not appear to be any significant banding of the showers and thunderstorms.

A large upper level low over the Gulf of Mexico was producing moderate southerly winds which were blowing across the western side of Potential Tropical Cyclone Nine.  Those winds were causing moderate vertical wind shear.  A small upper level ridge was developing between the upper low over the Gulf and another smaller upper low near Bermuda.  Winds were weaker under the ridge and that was the likely reason the stronger thunderstorms were in the northeastern part of the disturbance.  It is possible that a new center of circulation could develop near one of the clusters of thunderstorms.

Potential Tropical Cyclone Nine will move through an area somewhat favorable for intensification.  It will move over water where the Sea Surface Temperature is near 29°C.  The upper low over the Gulf of Mexico is forecast to move westward which would cause the vertical wind shear to decrease.  If the shear decreases, then a distinct low level center of circulation could develop.  If a distinct center forms, then the system would be designated as a tropical depression.  Potential Tropical Cyclone Nine has the potential to strengthen into a tropical storm during the next 24 to 48 hours.

The future track of Potential Tropical Cyclone Nine will depend on the place where a center of circulation forms and how strong the system becomes.  A stronger tropical cyclone would be steered by winds higher in the atmosphere.  If Potential Tropical Cyclone Nine strengthens significantly then the upper level low over the Gulf of Mexico and the developing upper level ridge will combine to the system toward the northwest during the next day or two.  A cold front moving southeast across the Great Lakes and Ohio River Valley could turn the system toward the northeast later in the weekend.  Under that scenario Potential Tropical Cyclone Nine would move across the Northwestern Bahamas on Friday.  It could approach southeast Florida on Saturday.

On the other hand, if Potential Tropical Cyclone Nine does not develop, or if it remains a weak tropical cyclone, then it would be steered by winds lower in the atmosphere.  In that case the system could be steered more toward the west-northwest and it could move across Florida into the Gulf of Mexico.   The guidance from numerical models is very divergent about the predicted future track of Potential Tropical Cyclone Nine.  In any case the system will bring some wind and rain to the Northwestern Bahamas and that will hinder efforts to recover from Hurricane Dorian.