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| #541088 (Received by flhurricane at: 10:47 PM 07.Sep.2012) TCDAT2 TROPICAL STORM LESLIE DISCUSSION NUMBER 35 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012 1100 PM AST FRI SEP 07 2012 SATELLITE IMAGERY AND REPORTS FROM NOAA P-3 AND G-IV HURRICANE HUNTER AIRCRAFT SHOW CHANGES IN THE STRUCTURE OF LESLIE THIS EVENING. THE STORM CURRENTLY LACKS AN INNER CORE...AS THE RADIUS OF MAXIMUM WINDS IS NOW ON THE ORDER OF 75 N MI. IN ADDITION... INFRARED AND MICROWAVE SATELLITE IMAGERY SHOW WELL-DEFINED CURVED CONVECTIVE BANDS OVER THE NORTHERN SEMICIRCLE AT A LARGE DISTANCE FROM THE CENTER. DROPSONDE DATA AND SFMR SURFACE WIND ESTIMATES SUPPORT AN INITIAL INTENSITY OF 55 KT...WHICH IS IN GOOD AGREEMENT WITH THE SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB. THE CENTRAL PRESSURE OF 983 MB IS BASED ON A COMBINATION OF AIRCRAFT AND NOAA BUOY DATA. THE INITIAL MOTION IS 350/3. LESLIE IS STILL EMBEDDED IN AN AREA OF WEAK STEERING CURRENTS IN THE MIDDLE OF THE SUBTROPICAL RIDGE. THE GLOBAL MODELS FORECAST THE RIDGE WEST OF LESLIE TO BREAK DOWN AS A LARGE DEEP-LAYER TROUGH AND ASSOCIATED SURFACE COLD FRONT MOVE ACROSS THE EASTERN UNITED STATES INTO THE WESTERN ATLANTIC. THE TRACK GUIDANCE IS IN GOOD AGREEMENT THAT DURING THE NEXT 48-72 HR LESLIE SHOULD GRADUALLY ACCELERATE NORTHWARD TO NORTH- NORTHEASTWARD...WITH THE CENTER PASSING EAST OF BERMUDA BETWEEN 36-48 HR. AFTER THAT...THE GUIDANCE IS IN GOOD AGREEMENT THAT LESLIE SHOULD CONTINUE NORTH-NORTHEASTWARD...BUT THERE IS SOME SPREAD IN THE FORWARD SPEED. THE ECMWF AND GFS MODELS SHOW LESLIE SLOWING AS IT GETS CAUGHT UP IN AN UPPER-LEVEL LOW NEAR NEWFOUNDLAND...WHILE THE CANADIAN AND UKMET MODELS SHOW A FASTER MOTION. THE LATTER PART OF THE NEW FORECAST TRACK COMPROMISES BETWEEN THESE EXTREMES AND IS NEAR THE CONSENSUS MODELS. IT IS SIMILAR TO THE PREVIOUS FORECAST THROUGH 72 HR AND A LITTLE LEFT OF THE PREVIOUS FORECAST AFTER THAT. THE INTENSITY FORECAST REMAINS COMPLICATED. ON THE PLUS SIDE... LESLIE SHOULD BE MOVING AWAY FROM THE COLD WATER IT HAS UPWELLED... AND THE VERTICAL WIND SHEAR IS FORECAST TO BE GENERALLY LIGHT THROUGH 72 HR. ON THE MINUS SIDE...THE CURRENT STRUCTURE IS LIKELY NOT CONDUCIVE FOR RAPID DEVELOPMENT...AND WATER VAPOR IMAGERY SHOWS THAT LESLIE WILL CONTINUE TO HAVE ISSUES WITH DRY AIR ENTRAINMENT. THE NEW INTENSITY FORECAST SHOW A SLOWER RATE OF DEVELOPMENT TO THE PEAK INTENSITY IN 72 HR THAN THE PREVIOUS FORECAST...CLOSE TO THE SHIPS MODEL AND BELOW THE INTENSITY CONSENSUS. AFTER 72 HR... INCREASING SHEAR AND THE ONSET OF EXTRATROPICAL TRANSITION SHOULD CAUSE WEAKENING. EXTRATROPICAL TRANSITION IS FORECAST TO BE COMPLETE BY 120 HR. THE WIND FIELD OF LESLIE...COMBINED WITH ITS EXPECTED SLOW MOTION... WILL 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. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 27.6N 62.3W 55 KT 65 MPH 12H 08/1200Z 28.2N 62.3W 55 KT 65 MPH 24H 09/0000Z 29.5N 62.2W 60 KT 70 MPH 36H 09/1200Z 31.0N 61.9W 65 KT 75 MPH 48H 10/0000Z 32.7N 61.3W 75 KT 85 MPH 72H 11/0000Z 37.0N 59.0W 80 KT 90 MPH 96H 12/0000Z 43.0N 55.0W 70 KT 80 MPH 120H 13/0000Z 48.0N 52.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ FORECASTER BEVEN |
