Tropical Storm COLIN

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TROPICAL STORM COLIN DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042010
1100 AM AST FRI AUG 06 2010

COLIN SHOWS A CLASSIC SHEAR PATTERN THIS MORNING WITH THE LOW-LEVEL
CENTER EXPOSED TO THE WEST OF THE MAIN CONVECTIVE MASS BY 20-25 KT
OF WESTERLY VERTICAL WIND SHEAR.  DVORAK AND AMSU SATELLITE
INTENSITY ESTIMATES HAVE NOT CHANGED SINCE THE PREVIOUS ADVISORY
AND REMAIN NEAR 35 KT.  BASED ON THIS...THE INITIAL INTENSITY
REMAINS 40 KT...AND THIS COULD BE A LITTLE GENEROUS.  AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE COLIN
AROUND 18Z TODAY.

JUST AFTER THE PREVIOUS ADVISORY...THE CENTER OF COLIN TOOK A SHARP
TURN TO THE RIGHT...AND IT HAS BEEN MOVING 065/6 FOR THE PAST
SEVERAL HOURS.  THIS IS LIKELY TO BE TEMPORARY...AS THE SYNOPTIC
PATTERN OF HIGHER PRESSURES TO THE EAST AND LOWER PRESSURES TO THE
WEST SUPPORT A MOTION TOWARD THE NORTH DURING THE NEXT 24-36 HR. 
THAT MOTION SHOULD BRING COLIN NORTH OF THE SUBTROPICAL RIDGE AXIS
INTO THE WESTERLIES...WHICH IN TURN SHOULD CAUSE THE CYCLONE TO MOVE
NORTHEASTWARD WITH AN INCREASING FORWARD SPEED.  THE TRACK GUIDANCE
IS IN GOOD AGREEMENT WITH THIS SCENARIO...BUT THERE REMAIN SOME
SPREAD IN THE SPEED BETWEEN THE SLOWER GFS AND THE FASTER NOGAPS. 
THE NEW FORECAST TRACK IS NUDGED TO THE EAST BASED ON THE INITIAL
POSITION AND MOTION AND IS IN BEST OVERALL AGREEMENT WITH THE UKMET
AND ECMWF.  SOME ADDITIONAL ADJUSTMENT MAY BE NECESSARY LATER
TODAY...DEPENDING ON HOW LONG COLIN CONTINUES THE CURRENT MOTION.
 
SHEAR FORECASTS FROM THE SHIPS AND THE DYNAMICAL MODELS SUGGEST THAT
THE CURRENT SHOULD SHOULD DECREASE DURING THE NEXT 12-24 HR...
ALTHOUGH THE SHIPS MODEL MAY BE OVERLY OPTIMISTIC WITH ITS FORECAST
OF 11 KT OF SHEAR BY 00Z.  AFTER THIS...COLIN IS LIKELY TO REMAIN
IN AN ENVIRONMENT FAVORABLE FOR STRENGTHENING UNTIL IT REACHES
STRONGER SHEAR IN THE MAIN BELT OF THE WESTERLIES IN ABOUT 72 HR. 
THE GFDL AND HWRF FORECAST COLIN TO BECOME A HURRICANE BY 72 HR...
WHILE THE SHIPS AND LGEM ARE LESS AGGRESSIVE.  THE FORECAST PEAK
INTENSITY OF 60 KT IS A COMPROMISE BETWEEN THESE EXTREMES IN
AGREEMENT WITH THE INTENSITY CONSENSUS.  EXTRATROPICAL TRANSITION
SHOULD BEGIN AT ABOUT 72 HR AND BE COMPLETE BY 96 HR...WITH THE
DYNAMICAL MODELS FORECASTING COLIN TO REMAIN A STRONG CYCLONE
THROUGH THAT PROCESS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      06/1500Z 27.1N  66.9W    40 KT
 12HR VT     07/0000Z 28.3N  66.9W    40 KT
 24HR VT     07/1200Z 30.2N  66.3W    45 KT
 36HR VT     08/0000Z 32.2N  65.4W    50 KT
 48HR VT     08/1200Z 34.5N  64.1W    55 KT
 72HR VT     09/1200Z 39.5N  60.0W    60 KT
 96HR VT     10/1200Z 45.0N  52.0W    55 KT...POST-TROP/EXTRATROP
120HR VT     11/1200Z 53.0N  41.5W    50 KT...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 
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