000 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