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Chill falls over the Atlantic as the official season heads towards close
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| #541503 (Received by flhurricane at: 4:53 AM 09.Sep.2012) TCDAT2 TROPICAL STORM LESLIE DISCUSSION NUMBER 40 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012 500 AM AST SUN SEP 09 2012 DEEP CONVECTION ASSOCIATED WITH LESLIE DECREASED IN COVERAGE LATE IN THE EVENING...HOWEVER A NEW BURST OF THUNDERSTORMS HAS FORMED JUST NORTH OF THE CENTER...AND IT IS NOW WRAPPING AROUND THE WESTERN PORTION OF THE CIRCULATION. THE LATEST DVORAK INTENSITY ESTIMATES RANGE FROM 45 TO 55 KT AND AN EARLIER ASCAT PASS SHOWED A LARGE AREA OF 40-45 KT WINDS. THE INITIAL INTENSITY IS MAINTAINED AT 55 KT...WHICH COULD BE A LITTLE GENEROUS. AS LESLIE MOVES NORTHWARD IT SHOULD FINALLY LEAVE THE AREA OF COOLER WATERS CAUSED BY UPWELLING DURING THE PAST SEVERAL DAYS. AS THIS OCCURS THE CYCLONE IS FORECAST TO BE IN A FAVORABLE UPPER-AIR ENVIRONMENT. THESE CONDITIONS FAVOR INTENSIFICATION...HOWEVER GIVEN THE CURRENT STRUCTURE OF THE CYCLONE AND ISSUES WITH DRY AIR ENTRAINMENT...LESLIE MAY HAVE SOME DIFFICULTY IN STRENGTHENING. THE NEW NHC FORECAST CALLS SOME INCREASE IN WIND SPEED...BUT LESS THAN IN THE PREVIOUS ADVISORY. LESLIE IS FORECAST TO BEGIN INTERACTING WITH A FRONTAL ZONE WITHIN 48 HOURS AND THE CYCLONE IS EXPECTED TO BECOME EXTRATROPICAL EARLY TUESDAY. THE EXTRATROPICAL LOW IS PREDICTED TO MAINTAIN ITS INTENSITY FOR A DAY OR SO BEFORE GRADUALLY WEAKENING OVER THE NORTH ATLANTIC. THE INITIAL MOTION IS 360 DEGREES AT 8 KT. LESLIE IS FORECAST TO BEGIN MOVING FASTER TOWARD THE NORTH AND NORTH-NORTHEAST AS A LARGE DEEP-LAYER TROUGH MOVES EASTWARD OFF THE EAST COAST OF THE UNITED STATES. THE TRACK MODEL GUIDANCE IS TIGHTLY CLUSTERED DURING THE FIRST 48 HOURS AND THE NHC TRACK IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. THE GLOBAL MODEL GUIDANCE HAS ONCE AGAIN TRENDED TOWARD A FASTER SOLUTION FOR THE 3 TO 5 DAY FORECAST PERIODS. THIS HAS RESULTED IN A SIGNIFICANT ADJUSTMENT TO THE TRACK FORECAST AT 72 THROUGH 120 H. HOWEVER...THE TRACK FORECAST FOR THE EXTRATROPICAL PORTION IS STILL SLOWER THAN THE MODEL CONSENSUS IN ORDER TO MAINTAIN SOME CONTINUITY WITH THE PREVIOUS ADVISORY. LONG-PERIOD SWELLS FROM LESLIE ARE EXPECTED TO PRODUCE ROUGH SURF AND LIFE-THREATENING RIP CURRENTS ON BERMUDA AND ALONG MUCH OF THE U.S. EAST COAST FOR THE NEXT FEW DAYS. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 30.8N 62.5W 55 KT 65 MPH 12H 09/1800Z 32.4N 62.3W 55 KT 65 MPH 24H 10/0600Z 34.5N 61.5W 60 KT 70 MPH 36H 10/1800Z 37.5N 60.2W 65 KT 75 MPH 48H 11/0600Z 42.0N 58.0W 65 KT 75 MPH 72H 12/0600Z 52.0N 50.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 13/0600Z 59.5N 35.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 14/0600Z 61.0N 15.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ FORECASTER BROWN |
