Friday, September 13, 2019

NOT AGAIN! - Tropical Storm Warnings Up for Bahama Islands Devastated by Dorian

Dr. Jeff Masters 
September 13, 2019, 
11:08 AM EDT 

Above: Visible GOES-16 satellite image of Potential Tropical Cyclone 9 (PTC 9) over The Bahamas at 10:40 am EDT September 13, 2019. Image credit: NOAA/RAMMB.

Long-suffering residents of the Northwest Bahamas—still coming to grips with the human and physical toll from catastrophic Hurricane Dorian—now face a tropical storm warning for a system predicted to develop into a tropical storm by Saturday. Update: A disturbance in the Southeast Bahamas, designated Potential Tropical Cyclone 9 (PTC 9) by the National Hurricane Center on Thursday, became Tropical Depression 9 with a 5 pm advisory from NHC. It is predicted to become Tropical Storm Humberto tonight or Saturday. The tropical storm warning for the Northwest Bahamas includes all areas except Andros Island. Tropical storm watches are up for a portion of the central east coast of Florida, as well. There is little change to the overall prognosis outlined below.

PTC 9 was bringing heavy rain showers and gusty winds to the east coast of Florida and The Bahamas on Friday morning, including the islands of the Northwest Bahamas hardest-hit by Hurricane Dorian earlier this month.  
on the western end of Grand Bahama Island, which was devastated by Dorian, recorded sustained winds of 28 mph, gusting to 32 mph, at 2 am EDT Friday morning. As of 11 am EDT Friday, the top surface winds found by the Hurricane Hunters in PTC 9 were just 25 mph, though the plane had not sampled the entire circulation yet. Update: The Hurricane Hunters found a weak center of circulation near the heaviest showers and thunderstorms (convection), prompting the upgrade to a tropical depression.

Satellite loops 
and data from the Bahamas radar and the Hurricane Hunters on Friday morning showed that PTC 9 did not have a well-defined surface circulation, but heavy thunderstorm activity was steadily growing in intensity, areal coverage, and organization. The system was tangled up with an upper-level trough off the west coast of Florida, and the upper-level winds associated with this trough were bringing dry air and moderate wind shear of 15 – 20 knots to the west side of PTC 9, inhibiting development. Sea surface temperatures (SSTs) in The Bahamas, though depressed by the passage of Hurricane Dorian, were still plenty warm for development--near 29°C (84°F).

The main threat from PTC 9 to the Northwest Bahamas is heavy rain and perhaps tropical-storm-force winds, as the system will have little time to intensify further before reaching the islands. Widespread rainfall of 2” to 4” is expected, with pockets of up to 6” possible. These conditions will hamper post-Dorian relief efforts, but will provide much-needed rain to the cisterns used to provide fresh water to the islands.

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