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| #540363 (Received by flhurricane at: 10:44 AM 05.Sep.2012) TCDAT2 TROPICAL STORM LESLIE DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012 1100 AM AST WED SEP 05 2012 THE VERTICAL SHEAR AFFECTING LESLIE HAS BEEN GRADUALLY DECREASING THIS MORNING...WHICH HAS ALLOWED A BANDING EYE FEATURE TO DEVELOP IN VISIBLE SATELLITE IMAGERY. HOWEVER...A 0944 UTC SSMIS MICROWAVE OVERPASS INDICATED THE MID-LEVEL EYE FEATURE WAS DISPLACED ABOUT 12-18 NMI EAST OF THE LOW-LEVEL CENTER. DVORAK SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS T3.5/55 KT FROM TAFB AND SAB...AND THE LATEST ADT ESTIMATE IS T4.3/72 KT. THE INITIAL INTENSITY OF 60 KT IS A BLEND OF THESE VALUES...AND LESLIE IS BEING HELD JUST BELOW HURRICANE INTENSITY DUE TO THE EASTWARD-TILTED VORTEX COLUMN. THE INITIAL MOTION ESTIMATE IS 360/02 BASED ON MICROWAVE AND VISIBLE SATELLITE FIXES. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. LESLIE IS EXPECTED TO WOBBLE SLOWLY ALONG A GENERAL NORTH-NORTHWESTWARD TRACK FOR THE NEXT 72 HOURS OR SO DUE TO A BLOCKING RIDGE TO THE NORTH AND EAST OF THE CYCLONE. AFTERWARDS...A DEEP-LAYER TROUGH IS FORECAST TO MOVE OUT OF SOUTHERN CANADA AND DIG SOUTHEASTWARD TO THE U.S. EAST COAST... WHICH SHOULD ACT TO ACCELERATE LESLIE TOWARD THE NORTH BY 96 HOURS...AND TOWARD THE NORTHEAST BY 120 HOURS. THE OFFICIAL FORECAST TRACK HAS BEEN NUDGED SLIGHTLY TO THE EAST OF THE PREVIOUS TRACK...BUT ONLY DUE TO THE MORE EASTWARD INITIAL POSITION...AND REMAINS NEAR THE LEFT SIDE OF THE GUIDANCE ENVELOPE BETWEEN THE CONSENSUS MODELS TVCA AND TV15. LESLIE IS VERY NEAR HURRICANE STRENGTH...AND CONDITIONS ARE EXPECTED TO BECOME QUITE FAVORABLE FOR ADDITIONAL INTENSIFICATION TO OCCUR THROUGH AT LEAST 96 HOURS. THE ONLY OBVIOUS INHIBITING FACTOR IS COLD UPWELLING BENEATH THE CYCLONE DUE TO ITS VERY SLOW FORWARD SPEED. IT IS POSSIBLE THAT LESLIE COULD INTENSIFY MORE QUICKLY THAN FORECAST FOR THE NEXT 48 HOURS OR SO...AND THEN LEVEL OFF IN 72-96 HOURS DUE TO UPWELLING. THE SHIPS AND LGEM MODELS CONTINUE TO SHOW SYMPTOMS OF NEGATIVE FEEDBACK CAUSED BY THE GFS MODEL 200 MB WARMING AFTER 72 HOURS. THE GFS...ECMWF... UKMET...AND HWRF MODELS GENERATE A VERY ROBUST HURRICANE THROUGHOUT THE FORECAST PERIOD...AND THIS STRENGTHENING TREND HAS BEEN FOLLOWED IN THIS ADVISORY. THE OFFICIAL INTENSITY FORECAST IS SLIGHTLY HIGHER THAN THE PREVIOUS ADVISORY...AND REMAINS ABOVE MOST OF THE INTENSITY GUIDANCE AFTER 72 HOURS. LESLIE IS A LARGE TROPICAL CYCLONE THAT IS FORECAST TO GROW IN SIZE OVER THE NEXT SEVERAL DAYS. THE WIND FIELD OF THE CYCLONE... COMBINED WITH ITS EXPECTED SLOW MOTION...WILL HELP TO GENERATE LARGE LONG-PERIOD SWELLS THAT WILL PROPAGATE AWAY FROM THE TROPICAL CYCLONE TOWARD BERMUDA AND MUCH OF THE U.S. EAST COAST FOR THE REMAINDER OF THIS WEEK. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 25.7N 62.8W 60 KT 70 MPH 12H 06/0000Z 26.0N 62.9W 65 KT 75 MPH 24H 06/1200Z 26.5N 63.0W 70 KT 80 MPH 36H 07/0000Z 26.8N 63.1W 75 KT 85 MPH 48H 07/1200Z 27.2N 63.4W 80 KT 90 MPH 72H 08/1200Z 29.0N 64.3W 85 KT 100 MPH 96H 09/1200Z 32.4N 64.7W 95 KT 110 MPH...NEAR BERMUDA 120H 10/1200Z 39.5N 62.0W 95 KT 110 MPH $$ FORECASTER STEWART |
