Tropical Storm LESLIE

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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
 
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