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Tropical Storm LESLIE (Text)

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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
 
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