[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 010244
TCDAT2

TROPICAL STORM LESLIE DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
1100 PM AST FRI AUG 31 2012

LESLIE IS PRODUCING A LARGE CENTRAL AREA OF CONVECTION WITH CLOUD
TOPS COLDER THAN -80C.  HOWEVER...AN SSM/IS OVERPASS AT 2318 UTC
AND A TRMM OVERPASS AT 0030 UTC INDICATED THAT THE CENTER IS STILL
DISPLACED TO THE NORTH OF THE CONVECTION DUE TO CONTINUING
NORTHERLY VERTICAL WIND SHEAR.  SATELLITE INTENSITY ESTIMATES ARE
55 KT FROM TAFB AND 45 KT FROM SAB....AND THE INITIAL INTENSITY
REMAINS 55 KT.  ALTHOUGH SHEAR CONTINUES...THE CIRRUS OUTFLOW IS
GOOD IN ALL DIRECTIONS EXCEPT TO THE NORTH.

THE INITIAL MOTION IS 295/18.  THE SUBTROPICAL RIDGE NORTH AND
NORTHEAST OF THE STORM SHOULD STEER LESLIE WEST-NORTHWESTWARD FOR
THE NEXT 36 HR.  AFTER THAT...THE CYCLONE IS LIKELY TO TURN
NORTHWESTWARD AND THEN NORTHWARD DUE TO A BREAK IN THE RIDGE
CREATED BY A DEVELOPING MID/UPPER-LEVEL LEVEL LOW PRESSURE
SYSTEM...CURRENTLY SEEN IN WATER VAPOR IMAGERY BETWEEN BERMUDA AND
THE EASTERN UNITED STATES.  THE FORECAST TRACK THROUGH 72 HR IS AN
UPDATE OF THE PREVIOUS TRACK AND LIES NEAR THE CENTER OF THE TRACK
GUIDANCE ENVELOPE.  THE GUIDANCE DIVERGES AFTER 72 HR AS LESLIE IS
EXPECTED TO MOVE INTO AN AREA OF LIGHT STEERING CURRENTS.  THE
GFS...GFDL...HWRF...AND CANADIAN MODELS SHOW A SLOW EASTWARD OR
NORTHEASTWARD MOTION DURING THIS PERIOD...WHILE THE ECMWF AND THE
FLORIDA STATE SUPERENSEMBLE SHOW A SLOW NORTHWESTWARD MOTION.
OVERALL...THE GUIDANCE ENVELOPE HAS SHIFTED A LITTLE TO THE EAST
AFTER 72 HR.  AS A RESULT...THE NEW FORECAST TRACK IS ALSO NUDGED A
LITTLE TO THE EAST AND SHOWS A SLOW NORTHWARD MOTION BY 120 HR.
HOWEVER...IT LIES ON THE LEFT SIDE OF THE GUIDANCE ENVELOPE TO THE
WEST OF THE CONSENSUS MODELS.

THE GLOBAL MODELS SUGGEST THAT SOME NORTHERLY SHEAR SHOULD PERSIST
FOR THE NEXT 24-48 HR...AND IT IS UNCLEAR IF LESLIE WILL FIND A
REALLY FAVORABLE ENVIRONMENT FOR DEVELOPMENT DURING THIS TIME.
FROM 48-96 HR...THE CYCLONE MOVES NORTH OF AN UPPER-LEVEL RIDGE AND
IS LIKELY TO ENCOUNTER MODERATE/STRONG WESTERLY SHEAR...WHICH AT
THE VERY LEAST SHOULD STOP DEVELOPMENT.  THE UPPER-LEVEL WINDS MAY
BECOME MORE FAVORABLE AFTER 96 HR...ALTHOUGH THE ECMWF STILL SHOWS
A RATHER HOSTILE ENVIRONMENT DURING THIS TIME.  THE NEW INTENSITY
FORECAST IS THE SAME AS THE PREVIOUS FORECAST...CALLING FOR SLOW
DEVELOPMENT THROUGH 48 HR...LITTLE CHANGE IN STRENGTH AT 72 AND 96
HR...AND SLIGHT STRENGTHENING FROM 96-120 HR.  THE FORECAST IS A
BLEND OF THE SHIPS MODEL AND THE INTENSITY CONSENSUS.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 17.4N  52.8W   55 KT  65 MPH
 12H  01/1200Z 18.3N  54.8W   60 KT  70 MPH
 24H  02/0000Z 19.7N  57.4W   60 KT  70 MPH
 36H  02/1200Z 21.1N  59.4W   65 KT  75 MPH
 48H  03/0000Z 22.6N  60.9W   70 KT  80 MPH
 72H  04/0000Z 25.0N  62.0W   70 KT  80 MPH
 96H  05/0000Z 26.5N  62.5W   70 KT  80 MPH
120H  06/0000Z 28.0N  62.5W   75 KT  85 MPH

$$
FORECASTER BEVEN



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