[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 062033
TCDAT4
TROPICAL STORM COLIN DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042010
500 PM AST FRI AUG 06 2010

THERE HAVE BEEN SOME CHANGES WITH COLIN AND THE NEAR-STORM
ENVIRONMENT SINCE THE LAST ADVISORY.  FIRST...THE WELL-DEFINED LOW
CLOUD SWIRL SEEN EARLIER HAS BECOME PART OF A LARGER ELONGATED
CIRCULATION WITH MULTIPLE SWIRLS ROTATING AROUND A MEAN CENTER.
SECOND...CIRRUS CLOUDS APPROACHING THE CENTER FROM THE SOUTHWEST
ARE MOVING AT 40 KT...SUGGESTING THAT THE VERTICAL WIND SHEAR HAS
INCREASED.  THIRD...LIKELY AS A RESULT OF THE INCREASED SHEAR...THE
CONVECTION HAS DECREASED NEAR THE CENTER.  DESPITE THESE NEGATIVE
FACTORS...AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS FOUND
43-KT WINDS AT 500 FT SOUTHEAST OF THE CENTER WITH ESTIMATED
SURFACE WINDS FROM THE SFMR OF 39 KT.  BASED ON THIS...THE INITIAL
INTENSITY REMAINS A POSSIBLY GENEROUS 40 KT.

AFTER THE TRACK EXCURSION NOTED EARLIER...THE MEAN CENTER OF THE
CIRCULATION HAS RESUMED A NORTHWARD MOTION OF 010/8.  THERE IS
LITTLE CHANGE TO THE TRACK FORECAST PHILOSOPHY.  COLIN IS MOVING
NORTHWARD BETWEEN THE SUBTROPICAL RIDGE AND A MID/UPPER-LEVEL LOW
NEAR 28N74W AS A DEEP-LAYER WESTERLY TROUGH MOVES ACROSS THE
NORTHEASTERN UNITED STATES.  ALL TRACK GUIDANCE AGREES THAT THE
CYCLONE SHOULD CONTINUE GENERALLY NORTHWARD OR NORTH-NORTHEASTWARD
FOR THE NEXT 36-48 HR...THEN TURN NORTHEASTWARD AT A FASTER FORWARD
SPEED AS IT REACHES THE MAIN BELT OF THE WESTERLIES.  THE NEW
FORECAST TRACK IS AN UPDATE OF THE PREVIOUS FORECAST.

LITTLE CHANGE IN STRENGTH IS LIKELY DURING THE NEXT 12-18 HR AS THE
40-KT UPPER-LEVEL WINDS IMPACT THE SYSTEM.  THE DYNAMICAL MODELS
FORECAST THAT THE SHEAR SHOULD DECREASE AFTER THAT...WHICH IF
CORRECT WOULD ALLOW COLIN TO STRENGTH.  THE GFDL AND HWRF MODELS
CONTINUE TO FORECAST COLIN TO BECOME A HURRICANE IN 60-72 HR...
WHILE THE SHIPS AND LGEM MODELS FORECAST A PEAK INTENSITY OF 50-55
KT.  THE NEW INTENSITY FORECAST IS THE SAME AS THE PREVIOUS
FORECAST...CALLING FOR A PEAK INTENSITY OF 60 KT IN 72 HR IN BEST
AGREEMENT WITH THE FLORIDA STATE SUPERENSEMBLE AND THE INTENSITY
CONSENSUS.  EXTRATROPICAL TRANSITION SHOULD BE UNDERWAY BY 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      06/2100Z 28.3N  66.8W    40 KT
 12HR VT     07/0600Z 29.5N  66.4W    40 KT
 24HR VT     07/1800Z 31.1N  65.7W    45 KT
 36HR VT     08/0600Z 32.8N  64.9W    50 KT
 48HR VT     08/1800Z 35.1N  64.0W    55 KT
 72HR VT     09/1800Z 41.0N  59.0W    60 KT
 96HR VT     10/1800Z 47.5N  48.5W    55 KT...POST-TROP/EXTRATROP
120HR VT     11/1800Z 56.0N  40.0W    50 KT...POST-TROP/EXTRATROP

$$
FORECASTER BEVEN

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