Tropical Storm BRET

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TROPICAL STORM BRET DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL022011
500 AM AST THU JUL 21 2011
 
DURING THE PAST 6 HOURS...CONVECTION WITH CLOUD TOPS TO -70C HAS
REDEVELOPED IN THE SOUTHERN QUADRANT AS NORTHERLY VERTICAL SHEAR
HAS ABATED SLIGHTLY. SATELLITE DATA-T NUMBERS FROM BOTH TAFB AND
SAB ARE T2.5/35 KT. SHIP WPGK PASSED THROUGH THE SOUTHERN QUADRANT
AROUND 0300Z...BEFORE CONVECTION HAD REDEVELOPED...AND REPORTED A
WIND SPEED OF 32 KT. BASED ON THESE DATA...THE INITIAL INTENSITY OF
BRET IS BEING MAINTAINED AT 35 KT.
 
THE MOTION ESTIMATE IS 050/07. THERE IS NO SIGNIFICANT CHANGE TO THE
PREVIOUS FORECAST TRACK OR REASONING. BRET IS GRADUALLY BEING
CAUGHT UP BY THE MID-LATITUDE WESTERLIES...BUT ITS FORWARD PROGRESS
IS BEING IMPEDED BY NORTHERLY WIND SHEAR THAT IS FORECAST TO BECOME
NORTHEASTERLY DURING THE NEXT 24 HOURS. AS A RESULT...ONLY SLOW
FORWARD PROGRESS IS EXPECTED FOR THE NEXT DAY OR SO UNTIL THE
CYCLONE WEAKENS AND IS STEERED MORE QUICKLY TO THE NORTHEAST BY
LOW- TO MID-LEVEL SOUTHWESTERLY FLOW ON THE NORTH SIDE OF A STRONG
SUBTROPICAL RIDGE LOCATED ALONG 30N LATITUDE. THE OFFICIAL FORECAST
TRACK IS SIMILAR TO BUT FASTER THAN THE PREVIOUS ADVISORY AND IS
BASICALLY DOWN THE MIDDLE OF THE TIGHTLY PACKED NHC MODEL GUIDANCE.
 
ALTHOUGH THE NORTHERLY SHEAR ACROSS BRET IS FORECAST TO INCREASE
DURING THE NEXT 12-18 HOURS...THE 200 MB WIND FIELDS ACTUALLY SHOW
THE SHEAR DECREASING BY 24 HOURS. FOR THIS REASON...BRET IS BEING
HELD ONTO AS A TROPICAL DEPRESSION A LITTLE LONGER THAN SOME OF THE
MODEL GUIDANCE IS FORECASTING. HOWEVER...AFTER 36 HOURS THE SEA
SURFACE TEMPERATURES BENEATH THE CYCLONE ARE FORECAST TO DROP BELOW
26C...AND THAT SHOULD RESULT IN DEGENERATION INTO A REMNANT LOW
PRESSURE SYSTEM. BY 48 HOURS...BRET IS FORECAST TO DISSIPATE
COMPLETELY OVER MUCH COLDER 20-22C SST WATER.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0900Z 33.1N  71.7W   35 KT  40 MPH
 12H  21/1800Z 34.4N  70.0W   30 KT  35 MPH
 24H  22/0600Z 36.2N  67.6W   30 KT  35 MPH
 36H  22/1800Z 37.8N  64.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  23/0600Z...DISSIPATED
 
$$
FORECASTER STEWART
 
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