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Tropical Storm LESLIE


ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
 
TROPICAL STORM LESLIE DISCUSSION NUMBER  39
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
1100 PM AST SAT SEP 08 2012

INFRARED SATELLITE IMAGERY SHOWS THAT THE CONVECTION ASSOCIATED WITH
LESLIE HAS AGAIN BECOME ASYMMETRIC...WITH MOST OF THE CONVECTION
CURRENTLY IN THE WESTERN SEMICIRCLE.  SATELLITE INTENSITY ESTIMATES
FROM TAFB AND SAB ARE 55 KT...AND A RECENT CIMSS SATELLITE
CONSENSUS ESTIMATE WAS 58 KT.  BASED ON THESE DATA...THE INITIAL
INTENSITY REMAINS 55 KT.

THE INITIAL MOTION IS 360/7.  A LARGE DEEP-LAYER TROUGH AND
ASSOCIATED SURFACE COLD FRONT ARE MOVING FROM THE EASTERN UNITED
STATES INTO THE NORTHWESTERN ATLANTIC.  INCREASING SOUTHERLY AND
SOUTHWESTERLY FLOW AHEAD OF THIS SYSTEM SHOULD STEER LESLIE TO THE
NORTH AND NORTH-NORTHEAST AT AN INCREASING FORWARD SPEED.  THE NEW
TRACK FORECAST IS SIMILAR TO THE PREVIOUS FORECAST THROUGH 48
HOURS.  AFTER THAT TIME...THE GLOBAL MODELS ARE NOW SHOWING A MUCH
FASTER NORTHWARD AND NORTHEASTWARD MOTION AS LESLIE UNDERGOES
EXTRATROPICAL TRANSITION.  THE GUIDANCE HAS SHIFTED ENOUGH THAT IT
IS IMPOSSIBLE TO FOLLOW IT AND MAINTAIN ANY CONTINUITY WITH THE
PREVIOUS FORECAST.  THUS...THE 72-120 HR FORECAST IS A COMPROMISE
BETWEEN THE SLOWER PREVIOUS FORECAST AND THE MUCH FASTER MODEL
GUIDANCE.  ADDITIONAL ADJUSTMENTS OF THIS PART OF THE FORECAST
TRACK MAY BE NECESSARY IF THE CURRENT MODEL TRENDS CONTINUE.

LESLIE CURRENTLY HAS A VERY IMPRESSIVE CIRRUS OUTFLOW PATTERN...AND
IT SHOULD ENCOUNTER A WARM WATER/LIGHT WIND SHEAR ENVIRONMENT FOR
THE NEXT 36-48 HR.  THIS SHOULD ALLOW SOME STRENGTHENING...
ALTHOUGH THE CURRENT STORM STRUCTURE AND ISSUES WITH DRY AIR
ENTRAINMENT ARGUE AGAINST RAPID DEVELOPMENT.  THE INTENSITY
GUIDANCE SHOWS A LITTLE LESS STRENGTHENING THAN 6 HR AGO...SO THE
NEW INTENSITY FORECAST IS REDUCED SLIGHTLY TO A PEAK INTENSITY OF
75 KT IN 48 HR.  THIS PART OF THE INTENSITY FORECAST IS A LITTLE
STRONGER THAN THE SHIPS MODEL AND THE INTENSITY CONSENSUS. 
EXTRATROPICAL TRANSITION SHOULD BEGIN AFTER 48 HR AND BE COMPLETE
BY 72-96 HR...WITH LESLIE FORECAST TO WEAKEN DURING THIS PROCESS.

THE WIND FIELD OF LESLIE...COMBINED WITH ITS EXPECTED SLOW MOTION...
WILL CONTINUE TO 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 AND INTO EARLY NEXT
WEEK.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/0300Z 30.1N  62.6W   55 KT  65 MPH
 12H  09/1200Z 31.3N  62.4W   60 KT  70 MPH
 24H  10/0000Z 33.2N  61.9W   65 KT  75 MPH
 36H  10/1200Z 35.3N  60.9W   70 KT  80 MPH
 48H  11/0000Z 38.5N  59.3W   75 KT  85 MPH
 72H  12/0000Z 46.0N  54.5W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  13/0000Z 49.0N  48.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  14/0000Z 51.5N  40.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Monday, 31-Dec-2012 12:09:34 UTC