[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 290849
TCDAT1

TROPICAL STORM OPHELIA DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
500 AM AST THU SEP 29 2011

DEEP CONVECTION HAS BEEN INCREASING NEAR AND JUST NORTH OF THE
ESTIMATED CENTER...AND THE AREA OF CONVECTION THAT WAS WELL
SOUTHEAST OF THE CENTER IS DIMINISHING. THIS INDICATES THAT OPHELIA
IS BECOMING BETTER ORGANIZED AND MAY BE STRENGTHENING...
HOWEVER...PENDING VISIBLE IMAGERY LATER THIS MORNING THE
INTENSITY...IS HELD AT 50 KT. ALTHOUGH WESTERLY SHEAR IS EXPECTED
TO CONTINUE TO AFFECT OPHELIA...SOME DECREASE IN SHEAR IS PREDICTED
IN 24 TO 36 HOURS AS AN UPPER-LEVEL RIDGE DEVELOPS OVER THE
TROPICAL CYCLONE. THIS EVOLUTION IS EXPECTED TO ALLOW OPHELIA TO
STRENGTHEN INTO A HURRICANE. THE OFFICIAL WIND SPEED FORECAST IS
SIMILAR TO THE PREVIOUS ONE AND LIES BETWEEN THE STATISTICAL-
DYNAMICAL GUIDANCE AT THE LOW END AND THE HWRF...GFDL...AND GFDN
MODELS AT THE HIGH END. WEAKENING SHOULD COMMENCE AFTER 72 HOURS AS
THE TROPICAL CYCLONE ENCOUNTERS SIGNIFICANTLY COOLER WATERS AND
INCREASING SHEAR. GLOBAL MODELS SHOW THE SYSTEM BECOMING EMBEDDED
IN A BAROCLINIC ZONE BY DAY 5...AND THE OFFICIAL FORECAST HAS
OPHELIA BECOMING AN EXTRATROPICAL CYCLONE BY THAT TIME.

THE INITIAL MOTION...330/6...IS ONLY A TAD FASTER THAN THE PREVIOUS
ESTIMATE.  THERE HAVE BEEN NO IMPORTANT CHANGES TO THE TRACK
FORECAST SCENARIO...AND THE MODELS REMAIN IN FARILY GOOD AGREEMENT
THROUGH THE FIRST HALF OF THE FORECAST PERIOD.  OPHELIA SHOULD MOVE
FASTER TOWARD THE NORTH-NORTHWEST AND NORTH OVER THE NEXT COUPLE OF
DAYS ALONG THE SOUTHWESTERN SIDE OF A SUBTROPICAL HIGH PRESSURE
AREA.  THEN...THE CYCLONE SHOULD TURN TOWARD THE NORTH-NORTHEAST
AND ACCELERATE AS IT MOVES IN THE FLOW ON THE EASTERN SIDE OF A
LARGE MID-LEVEL TROUGH NEAR THE U.S. EAST COAST.  NEAR THE END OF
THE FORECAST PERIOD...THE TRACK GUIDANCE BECOMES MORE DIVERGENT AS
THE DYNAMICAL MODELS DIFFER ON HOW OPHELIA WILL INTERACT WITH A
HIGH-LATITUDE EXTRATROPICAL CYCLONE.  THE OFFICIAL TRACK FORECAST
IS VERY CLOSE TO THE PREVIOUS ONE...AND ROUGHLY BETWEEN THE
MULTI-MODEL CONSENSUS AND THE LATEST ECMWF TRACK.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 20.0N  61.1W   50 KT  60 MPH
 12H  29/1800Z 21.1N  61.6W   55 KT  65 MPH
 24H  30/0600Z 22.8N  62.4W   60 KT  70 MPH
 36H  30/1800Z 24.9N  62.9W   70 KT  80 MPH
 48H  01/0600Z 27.8N  63.0W   75 KT  85 MPH
 72H  02/0600Z 35.5N  61.0W   75 KT  85 MPH
 96H  03/0600Z 46.5N  55.0W   55 KT  65 MPH
120H  04/0600Z 54.0N  44.0W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
FORECASTER PASCH


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