[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 210300
TCDAT1

TROPICAL STORM OPHELIA DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
1100 PM EDT TUE SEP 20 2011

THE LOW OVER THE TROPICAL ATLANTIC HAS FINALLY COALESCED ABOUT A
SINGLE CIRCULATION CENTER AND HAS ENOUGH ORGANIZED DEEP CONVECTION
TO BE CONSIDERED A TROPICAL CYCLONE. AN ASCAT PASS JUST BEFORE 00Z
SHOWED AN AREA OF 35 KT WINDS NORTH OF THE CENTER...AND THAT IS THE
INITIAL INTENSITY FOR THIS ADVISORY. THE SATELLITE PRESENTATION OF
OPHELIA IS STILL A LITTLE RAGGED...WITH CONVECTIVE BANDS LOCATED
WELL NORTHEAST AND SOUTH OF THE STILL CONSOLIDATING CENTER. WHILE
OPHELIA WILL BE MOVING OVER WARM WATERS THROUGH THE PERIOD...THE
SHEAR IS EXPECTED TO REMAIN AROUND 15 KT OR SO OVER THE NEXT COUPLE
OF DAYS.  AFTER THAT TIME...THE SHEAR SHOULD INCREASE AND BECOME
MORE WESTERLY AS THE GLOBAL MODELS SHOW AN UPPER-LEVEL LOW FORMING
NORTH OF PUERTO RICO. GIVEN THE MARGINAL ENVIRONMENT AND THE
SOMEWHAT SPRAWLING NATURE OF THE CYCLONE AT THIS TIME...ONLY MODEST
STRENGTHENING IS SHOWN IN THE SHORT TERM. BEYOND 36 HOURS...LITTLE
CHANGE IN STRENGTH IS FORECAST...FOLLOWED BY WEAKENING LATE IN THE
PERIOD. THE NHC FORECAST IS NEAR OR A LITTLE ABOVE THE IVCN
INTENSITY CONSENSUS THROUGH THE PERIOD.

THE INITIAL MOTION ESTIMATE IS A RATHER UNCERTAIN 270/8...DUE TO THE
RECENT REFORMATION OF THE CENTER. OPHELIA IS CURRENTLY BEING
STEERED BY THE SUBTROPICAL RIDGE TO ITS NORTH...AND A WESTWARD
MOTION IS EXPECTED OVER THE NEXT COUPLE OF DAYS AS THE RIDGE BUILDS
WESTWARD. AFTER THAT TIME...THE RIDGE BEGINS TO WEAKEN AS A LARGE
MID/UPPER-LEVEL CLOSED LOW DEVELOPS OVER THE SOUTHEASTERN UNITED
STATES...WHICH SHOULD RESULT IN A TURN TOWARD THE WEST-NORTHWEST
AND A DECREASE IN FORWARD SPEED LATE IN THE PERIOD. THE NHC TRACK
FORECAST LIES TO THE RIGHT OF THE MULTI-MODEL CONSENSUS THROUGH THE
PERIOD...BUT IS A LITTLE TO THE LEFT OF THE GFS AND ECMWF MODELS.

FORECAST POSITIONS AND MAX WINDS

INIT  21/0300Z 12.2N  40.1W   35 KT  40 MPH
 12H  21/1200Z 12.4N  42.2W   40 KT  45 MPH
 24H  22/0000Z 12.7N  44.9W   45 KT  50 MPH
 36H  22/1200Z 12.9N  47.7W   45 KT  50 MPH
 48H  23/0000Z 13.2N  50.5W   45 KT  50 MPH
 72H  24/0000Z 15.0N  55.5W   45 KT  50 MPH
 96H  25/0000Z 17.0N  60.0W   40 KT  45 MPH
120H  26/0000Z 19.0N  64.0W   40 KT  45 MPH

$$
FORECASTER BRENNAN



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