Tag Archives: Potential Tropical Cyclone Nine

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.

Tropical Storm Harvey Develops East of Barbados

A reconnaissance plane found that a center of circulation and winds to tropical storm force had developed in a tropical wave previously designated as Invest 91L and Potential Tropical Cyclone Nine.  Based on data collected by the recon plane the National Hurricane Center named the system Tropical Storm Harvey on Thursday afternoon.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Harvey was located at latitude 13.0°N and longitude 55.8°W which put it about 250 miles (400 km) east of Barbados.  Harvey was moving toward the west at 18 m.p.h. (30 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1004 mb.

A Tropical Storm Warning is in effect for Martinique, Barbados, St. Vincent and the Grenadines, and St. Lucia.  A Tropical Storm Watch is in effect for Dominica.

The circulation of Tropical Storm Harvey became better organized on Thursday.  A low level center of circulation developed and bands of showers and thunderstorms began to revolve around the center.  Intermittent bursts of thunderstorms occurred near and to the west of the center of circulation.  The circulation of Tropical Storm Harvey is asymmetrical.  Most of the stronger thunderstorms are occurring in the western half of the circulation.  The bands in the eastern half of the circulation consist primarily of showers and low clouds.  Thunderstorms near the core of Harvey were generating some upper level divergence which was pumping mass away to the south and west of the tropical storm.

Tropical Storm Harvey will be moving through an environment that will be somewhat favorable for intensification.  Harvey will move over water where the Sea Surface Temperature is near 29°C.  An upper level ridge northeast of Puerto Rico is producing northeasterly winds which are blowing toward the top of Tropical Storm Harvey.  Those winds are producing moderate vertical wind shear which is probably the cause of the asymmetrical distribution of thunderstorms.  Tropical Storm Harvey is likely to get better organized on Friday and it could strengthen.  The intensity guidance is mixed.  Some guidance forecasts that Harvey will become a hurricane as it moves over the Caribbean Sea, while other guidance weaken the tropical storm back to a tropical wave.  So far, the guidance has underpredicted the strength of Tropical Storm Harvey and so strengthen would seem more likely.

Tropical Storm Harvey is being steered quickly toward the west by the subtropical high over the Atlantic Ocean.  A general westerly or west-northwesterly track is forecast for the next few days.  On its anticipate track Tropical Storm Harvey could reach Barbados in about 12 hours.  Harvey could also reach Martinique, St. Lucia, St. Vincent and the Grenadines on Friday.  Tropical Storm Harvey will bring gusty winds and locally heavy rain to those islands when it moves over them.