000 WTNT42 KNHC 210859 TCDAT2 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