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| #541432 (Received by flhurricane at: 10:38 PM 08.Sep.2012) TCDAT2 TROPICAL STORM LESLIE DISCUSSION NUMBER 39 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012 1100 PM AST SAT SEP 08 2012 INFRARED SATELLITE IMAGERY SHOWS THAT THE CONVECTION ASSOCIATED WITH LESLIE HAS AGAIN BECOME ASYMMETRIC...WITH MOST OF THE CONVECTION CURRENTLY IN THE WESTERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 55 KT...AND A RECENT CIMSS SATELLITE CONSENSUS ESTIMATE WAS 58 KT. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 55 KT. THE INITIAL MOTION IS 360/7. A LARGE DEEP-LAYER TROUGH AND ASSOCIATED SURFACE COLD FRONT ARE MOVING FROM THE EASTERN UNITED STATES INTO THE NORTHWESTERN ATLANTIC. INCREASING SOUTHERLY AND SOUTHWESTERLY FLOW AHEAD OF THIS SYSTEM SHOULD STEER LESLIE TO THE NORTH AND NORTH-NORTHEAST AT AN INCREASING FORWARD SPEED. THE NEW TRACK FORECAST IS SIMILAR TO THE PREVIOUS FORECAST THROUGH 48 HOURS. AFTER THAT TIME...THE GLOBAL MODELS ARE NOW SHOWING A MUCH FASTER NORTHWARD AND NORTHEASTWARD MOTION AS LESLIE UNDERGOES EXTRATROPICAL TRANSITION. THE GUIDANCE HAS SHIFTED ENOUGH THAT IT IS IMPOSSIBLE TO FOLLOW IT AND MAINTAIN ANY CONTINUITY WITH THE PREVIOUS FORECAST. THUS...THE 72-120 HR FORECAST IS A COMPROMISE BETWEEN THE SLOWER PREVIOUS FORECAST AND THE MUCH FASTER MODEL GUIDANCE. ADDITIONAL ADJUSTMENTS OF THIS PART OF THE FORECAST TRACK MAY BE NECESSARY IF THE CURRENT MODEL TRENDS CONTINUE. LESLIE CURRENTLY HAS A VERY IMPRESSIVE CIRRUS OUTFLOW PATTERN...AND IT SHOULD ENCOUNTER A WARM WATER/LIGHT WIND SHEAR ENVIRONMENT FOR THE NEXT 36-48 HR. THIS SHOULD ALLOW SOME STRENGTHENING... ALTHOUGH THE CURRENT STORM STRUCTURE AND ISSUES WITH DRY AIR ENTRAINMENT ARGUE AGAINST RAPID DEVELOPMENT. THE INTENSITY GUIDANCE SHOWS A LITTLE LESS STRENGTHENING THAN 6 HR AGO...SO THE NEW INTENSITY FORECAST IS REDUCED SLIGHTLY TO A PEAK INTENSITY OF 75 KT IN 48 HR. THIS PART OF THE INTENSITY FORECAST IS A LITTLE STRONGER THAN THE SHIPS MODEL AND THE INTENSITY CONSENSUS. EXTRATROPICAL TRANSITION SHOULD BEGIN AFTER 48 HR AND BE COMPLETE BY 72-96 HR...WITH LESLIE FORECAST TO WEAKEN DURING THIS PROCESS. THE WIND FIELD OF LESLIE...COMBINED WITH ITS EXPECTED SLOW MOTION... WILL CONTINUE TO GENERATE LONG-PERIOD SWELLS THAT WILL PRODUCE LARGE WAVES AND LIFE-THREATENING RIP CURRENTS ON BERMUDA AND ALONG MUCH OF THE U.S. EAST COAST THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 30.1N 62.6W 55 KT 65 MPH 12H 09/1200Z 31.3N 62.4W 60 KT 70 MPH 24H 10/0000Z 33.2N 61.9W 65 KT 75 MPH 36H 10/1200Z 35.3N 60.9W 70 KT 80 MPH 48H 11/0000Z 38.5N 59.3W 75 KT 85 MPH 72H 12/0000Z 46.0N 54.5W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 13/0000Z 49.0N 48.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 14/0000Z 51.5N 40.5W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ FORECASTER BEVEN |
