[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 310241
TCDAT2

TROPICAL STORM LESLIE DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
1100 PM EDT THU AUG 30 2012

CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY SHOW THAT THE CENTER OF
LESLIE IS LOCATED TO THE NORTHEAST OF THE MAIN CONVECTIVE
MASS...MOST LIKELY DUE TO LIGHT/MODERATE NORTHEASTERLY VERTICAL
WIND SHEAR.  SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM TAFB AND
SAB.  IN ADDITION...NOAA BUOY 41041 REPORTED 1004 MB AND
NORTHWESTERLY WINDS OF 20-25 KT AS THE CENTER PASSED TO THE NORTH.
BASED ON THESE DATA...THE INITIAL INTENSITY IS INCREASED TO 45 KT.

THE INITIAL MOTION IS 280/16.  LESLIE IS CURRENTLY ON THE SOUTH SIDE
OF THE SUBTROPICAL RIDGE...WHICH SHOULD STEER THE SYSTEM GENERALLY
WEST-NORTHWESTWARD FOR THE NEXT 48 HR OR SO.  AFTER THAT...THE
GLOBAL MODELS ARE IN GOOD AGREEMENT THAT A MID-/UPPER-LEVEL
SHORTWAVE TROUGH...CURRENTLY SEEN IN WATER VAPOR IMAGERY MOVING OFF
OF THE COAST OF THE NORTHEASTERN UNITED STATES...SHOULD DEVELOP
INTO A CUT-OFF LOW BETWEEN BERMUDA AND THE BAHAMAS.  THIS LOW IS
FORECAST TO BREAK THE SUBTROPICAL RIDGE AT THE MID-/UPPER-LEVELS...
AND EXTEND FAR ENOUGH VERTICALLY DOWNWARD TO WEAKEN THE RIDGE AT
700-850 MB.  THIS EVOLUTION SHOULD CAUSE LESLIE TO GRADUALLY TURN
NORTHWARD ON THE EASTERN SIDE OF THE CUT-OFF LOW AFTER THE 48 HR
POINT.  THE TRACK GUIDANCE IS IN GOOD AGREEMENT WITH THIS
SCENARIO...AND THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS
TRACK THROUGH 96 HR.  IT SHOULD BE NOTED THAT THE TRACK GUIDANCE
STARTS TO DIVERGE AT 120 HR REGARDING HOW QUICKLY LESLIE SHOULD
ENCOUNTER THE WESTERLIES...AND BASED ON THIS SPREAD...THE TRACK
FORECAST CALLS FOR A SLOWER AND MORE NORTHERLY MOTION NEAR THAT
TIME.

THE GLOBAL MODELS SUGGEST THAT LESLIE SHOULD REMAIN IN AN
ENVIRONMENT OF LIGHT/MODERATE EASTERLY SHEAR FOR THE NEXT 36-48
HR...WHICH SHOULD ALLOW FOR GRADUAL DEVELOPMENT.  AFTER THAT
TIME...THE CYCLONE IS FORECAST TO ENCOUNTER SIGNIFICANT
SOUTHWESTERLY UPPER-LEVEL WINDS ASSOCIATED WITH THE CUT-OFF
LOW...WHICH IS EXPECTED TO CAUSE ENOUGH SHEAR TO SLOW OR HALT
INTENSIFICATION.  THE INTENSITY GUIDANCE IS FORECASTING A LITTLE
LESS STRENGTHENING THAN FOR THE PREVIOUS ADVISORY...MOST NOTABLY
AFTER 48 HR.  THE NEW INTENSITY FORECAST IS A BLEND OF THE PREVIOUS
FORECAST AND THE CURRENT SHIPS MODEL...SHOWING LESLIE BECOMING A
HURRICANE BY 24 HR AND SHOWING LITTLE CHANGE IN STRENGTH FROM
72-120 HR.

THE GLOBAL MODELS SHOW THIS SYSTEM BECOMING VERY LARGE...WHICH IS
REFLECTED IN THE CURRENT WIND FIELD FORECAST.  AN ADDITIONAL
INCREASE IN SIZE APPEARS LIKELY AFTER 72 HR.


FORECAST POSITIONS AND MAX WINDS

INIT  31/0300Z 14.7N  46.8W   45 KT  50 MPH
 12H  31/1200Z 15.5N  49.0W   55 KT  65 MPH
 24H  01/0000Z 16.7N  51.7W   65 KT  75 MPH
 36H  01/1200Z 17.9N  54.4W   75 KT  85 MPH
 48H  02/0000Z 19.3N  56.8W   80 KT  90 MPH
 72H  03/0000Z 22.5N  60.5W   85 KT 100 MPH
 96H  04/0000Z 26.5N  61.5W   85 KT 100 MPH
120H  05/0000Z 29.0N  61.5W   85 KT 100 MPH

$$
FORECASTER BEVEN
 
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