[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 031438
TCDAT4
TROPICAL STORM COLIN DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042010
1100 AM EDT TUE AUG 03 2010

COLIN HAS A VERY RAGGED APPEARANCE THIS MORNING.  THE CONVECTIVE
BANDING SEEN EARLIER HAS WEAKENED...LEAVING A SMALL CONVECTIVE MASS
NEAR THE CENTER AND A SECOND CONVECTIVE MASS TO THE NORTH.
SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM TAFB AND 30 KT FROM
SAB...AND BASED ON THIS THE INITIAL INTENSITY REMAINS 35 KT.  IT
SHOULD BE NOTED THAT IT IS HARD TO FIND WESTERLY WINDS IN THE LOW
CLOUD MOTIONS SOUTH OF THE CENTRAL CONVECTION...AND THERE IS SOME
QUESTION AS TO WHETHER COLIN STILL HAS A CLOSED CIRCULATION.

THE SYSTEM HAS TURNED A LITTLE TO THE LEFT DURING THE PAST SEVERAL
HOURS.  THE INITIAL MOTION IS 280/21...AND THE SHORT-TERM MOTION
MAY BE EVEN FASTER.  COLIN IS ON THE SOUTH SIDE OF THE LOW/
MID-LEVEL BERMUDA HIGH...AND IN 48-72 HR SHOULD BE APPROACHING A
WEAKNESS OR BREAK IN THE HIGH CAUSED BY A MID/UPPER-LEVEL TROUGH
NEAR THE SOUTHEASTERN COAST OF THE UNITED STATES.  THIS PATTERN
SHOULD INITIALLY STEER COLIN RAPIDLY TOWARD THE WEST-NORTHWEST...
FOLLOWED BY A TURN TOWARD THE NORTHWEST WITH A DECREASE IN FORWARD
SPEED AFTER 48 HR.  THE MODEL GUIDANCE GENERALLY AGREES WITH THIS
SCENARIO.  HOWEVER...THERE IS A CONSIDERABLE SPREAD IN THE TRACKS
BY THE END OF THE FORECAST PERIOD.  THE GFDL AND HWRF FORECAST AN
EAST OF NORTH MOTION ON THE RIGHT EDGE OF THE GUIDANCE ENVELOPE BY
120 HR...WHILE THE CANADIAN AND GFDN ARE ON THE LEFT EDGE WITH NO
NORTHWARD TURN BEFORE 120 HR.  THE NEW FORECAST TRACK IS SHIFTED
60-90 N MI TO THE SOUTHWEST BASED ON THE INITIAL POSITION AND
MOTION.  IT IS IN BEST AGREEMENT WITH THE ECMWF AND LIES TO THE
LEFT OF THE CONSENSUS MODELS AND THE CENTER OF THE GUIDANCE
ENVELOPE.

CURRENTLY...COLIN IS EXPERIENCING WESTERLY VERTICAL SHEAR LIKELY
CAUSED BY THE LOWER PART OF THE STORM OUTRUNNING THE UPPER PART.
THIS IS FORECAST TO CONTINUE FOR THE NEXT 24-36 HR DUE TO THE RAPID
MOTION.  AFTER THAT TIME...THE SYSTEM IS EXPECTED TO ENCOUNTER
INCREASING UPPER-LEVEL WESTERLY WINDS CAUSED BY THE WESTERN
ATLANTIC TROUGH.  THIS PATTERN DOES NOT APPEAR FAVORABLE FOR
SIGNIFICANT STRENGTHENING...AND THE ONLY INTENSITY GUIDANCE THAT
CURRENTLY CALLS FOR COLIN TO BECOME A HURRICANE IS CLIMATOLOGY/
PERSISTENCE.  GIVEN THE CURRENT TRENDS AND THE FORECAST SHEAR...THE
INTENSITY FORECAST IS A LITTLE WEAKER THAN THE PREVIOUS FORECAST...
WITH AN INTENSITY OF 45 KT THROUGH MOST OF THE FORECAST PERIOD.  AN
ALTERNATIVE SCENARIO IS THAT COLIN COULD DEGENERATE TO AN OPEN WAVE
DUE TO A COMBINATION OF ITS RAPID MOTION AND WESTERLY SHEAR.

INTERESTS IN THE NORTHERN LEEWARD ISLANDS AND THE VIRGIN ISLANDS
SHOULD FOLLOW THE PROGRESS OF COLIN.

FORECAST POSITIONS AND MAX WINDS

INITIAL      03/1500Z 14.2N  49.5W    35 KT
 12HR VT     04/0000Z 15.0N  52.7W    40 KT
 24HR VT     04/1200Z 16.5N  56.6W    45 KT
 36HR VT     05/0000Z 18.3N  60.4W    45 KT
 48HR VT     05/1200Z 20.2N  63.7W    45 KT
 72HR VT     06/1200Z 23.0N  67.5W    45 KT
 96HR VT     07/1200Z 26.5N  69.5W    45 KT
120HR VT     08/1200Z 29.0N  70.5W    50 KT

$$
FORECASTER BEVEN



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