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| #540837 (Received by flhurricane at: 10:35 PM 06.Sep.2012) TCDAT2 HURRICANE LESLIE DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012 1100 PM AST THU SEP 06 2012 THERE HAS BEEN NO SIGNIFICANT CHANGE IN THE SATELLITE APPEARANCE OF LESLIE DURING THE PAST SEVERAL HOURS...WITH THE SYSTEM CONTINUING TO FEATURE A CENTRAL DENSE OVERCAST WITH CLOUD TOPS COLDER THAN -70C. HOWEVER...MICROWAVE IMAGES PRIOR TO 0000 UTC DID NOT SHOW A WELL-DEFINED EYE OR EYEWALL. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 65 KT...WHILE SATELLITE CONSENSUS INTENSITY ESTIMATES FROM CIMSS ARE 60-65 KT. THE INITIAL INTENSITY REMAINS 65 KT FOR THIS ADVISORY. THE CIRRUS OUTFLOW IS GOOD IN THE EASTERN SEMICIRCLE AND IMPROVING IN THE WESTERN SEMICIRCLE. LESLIE HAS MOVED LITTLE DURING THE PAST SEVERAL HOURS AS IT REMAINS IN AN AREA OF LIGHT-TO-NON-EXISTENT STEERING CURRENTS. WATER VAPOR IMAGERY SHOWS A SHORTWAVE RIDGE IN THE WESTERLIES NORTH OF THE HURRICANE. THIS FEATURE IS EXPECTED TO MOVE EAST DURING THE NEXT 12-24 HR AND ALLOW LESLIE TO BEGIN A SLOW NORTHWARD MOTION. IN THE LONGER TERM...THE GLOBAL MODELS FORECAST A DEEP-LAYER TROUGH AND ASSOCIATED SURFACE FRONTAL SYSTEM TO MOVE EASTWARD THROUGH THE EASTERN UNITED STATES AND REACH THE WESTERN ATLANTIC BY 72 HR. THIS SYSTEM SHOULD STEER LESLIE NORTHWARD AND THEN EVENTUALLY NORTH-NORTHEASTWARD. HOWEVER...THERE IS SOME SPREAD IN THE GUIDANCE IN THE FORWARD SPEED...WITH THE CANADIAN MODEL NOTABLY FASTER THAN THE OTHER GUIDANCE...AND THE GFS SOMEWHAT SLOWER THAN THE OTHER GUIDANCE. THE FORECAST TRACK AFTER 36 HR COMPROMISES BETWEEN THESE EXTREMES AND LIES NEAR THE VARIOUS CONSENSUS MODELS. THE GUIDANCE ENVELOPE HAS CHANGED LITTLE SINCE THE LAST ADVISORY... AND THUS THE NEW FORECAST TRACK IS CLOSE TO THE PREVIOUS FORECAST. LESLIE HAS MOVED SLOWLY ENOUGH FOR THE PAST TWO DAYS TO HAVE UPWELLED COLD OCEAN WATER TO THE SURFACE. REPORTS FROM NOAA BUOY 41049 INDICATE THAT THE SEA SURFACE TEMPERATURE HAS DECREASED FROM 29C TO 26C-27C...WHILE MICROWAVE-BASED SEA SURFACE TEMPERATURE ESTIMATES SUGGEST TEMPERATURES OF 24C-25C UNDER THE CORE OF THE HURRICANE. AT BEST...LITTLE INTENSIFICATION SHOULD OCCUR UNTIL LESLIE MOVES NORTH OF THE COLD WATER...AND SOME WEAKENING IS POSSIBLE. THE NEW INTENSITY FORECAST FROM 12-36 HR IS REDUCED FROM THAT OF THE PREVIOUS ADVISORY BASED ON THE PRESENCE OF THE COLD WATER. FROM 36-72 HR...LESLIE SHOULD MOVE OVER WARMER WATERS AND STRENGTHEN...AND THE NEW FORECAST IS SIMILAR TO THE PREVIOUS FORECAST DURING THIS TIME. INCREASING SHEAR AND THE START OF EXTRATROPICAL TRANSITION SHOULD LEAD TO WEAKENING AFTER THE 72 HR POINT. 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 FOR THE REMAINDER OF THIS WEEK. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 26.5N 62.2W 65 KT 75 MPH 12H 07/1200Z 26.8N 62.2W 65 KT 75 MPH 24H 08/0000Z 27.2N 62.4W 65 KT 75 MPH 36H 08/1200Z 28.0N 62.6W 70 KT 80 MPH 48H 09/0000Z 29.3N 62.6W 80 KT 90 MPH 72H 10/0000Z 33.0N 61.5W 90 KT 105 MPH 96H 11/0000Z 37.0N 59.0W 80 KT 90 MPH 120H 12/0000Z 43.0N 55.5W 70 KT 80 MPH $$ FORECASTER BEVEN |
