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| #366757 (Received by flhurricane at: 10:43 PM 06.Aug.2010) TCDAT4 TROPICAL STORM COLIN DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042010 1100 PM AST FRI AUG 06 2010 COLIN IS A SHEARED CYCLONE WITH INCREASING CONVECTION NEAR AND TO THE EAST OF THE CENTER AT THIS TIME. THIS COULD GIVE AN IMPRESSION OF A STRONGER CYCLONE BUT FLUCTUATIONS IN CONVECTION ARE TYPICAL IN SHEARED SYSTEMS. THE STRONG UPPER-LEVEL WINDS CURRENTLY OVER THE CYCLONE WILL PROBABLY SEPARATE THE CENTER FROM THE THUNDERSTORM ACTIVITY AGAIN SOON. THEREFORE...THE INITIAL INTENSITY IS KEPT AT 40 KNOTS. ANOTHER RECONNAISSANCE PLANE WILL CHECK COLIN IN SEVERAL HOURS. COLIN HAS A SMALL WINDOW OF OPPORTUNITY TO GATHER SOME STRENGTH WITHIN THE NEXT DAY OR SO...IF THE SHEAR RELAXES A BIT AS DIAGNOSED BY THE SHIPS MODEL. IN FACT...IF THE CURRENT INCREASE IN CONVECTION CONTINUES OR PERSIST IT COULD MEAN THAT THE SHEAR IS ALREADY RELAXING AND SLIGHT INTENSIFICATION IS ABOUT TO BEGIN. THE OFFICIAL FORECAST ASSUMES THAT THE SHEAR WILL RELAX A BIT AND CALLS FOR A SMALL INCREASE IN INTENSITY. BY 96 HOURS...COLIN SHOULD BE EXTRATROPICAL AND THEN BECOME ABSORBED BY A LARGER CYCLONE. THE INTENSIFICATION SHOWN IN BOTH THE GFDL AND HWRF MODELS OCCURS LATE IN THE FORECAST PERIOD. THIS DOES NOT SEEM TO BE REALISTIC BECAUSE BY THEN...THE CYCLONE IS EXPECTED TO BE REACHING COOLER WATERS AND BECOMING EXTRATROPICAL. THE CENTER IS CLEARLY OBSERVED ON THE WESTERN EDGE OF THE CONVECTION AND ONE CAN OBTAIN A GOOD ESTIMATE OF THE INITIAL MOTION...WHICH IS TOWARD THE NORTH OR 010 DEGREES AT 8 KNOTS. COLIN IS ALREADY ON THE WESTERN EDGE OF THE SUBTROPICAL RIDGE AND IS NEARING THE MID-LATITUDE WESTERLIES. THEREFORE...THE CYCLONE SHOULD GRADUALLY TURN MORE TO THE NORTH-NORTHEAST WITH SOME INCREASE IN FORWARD SPEED. THERE IS GOOD CONFIDENCE IN THE FORECAST BECAUSE THE TRACK GUIDANCE IS PACKED AND THE OFFICIAL FORECAST IS IN THE MIDDLE OF THE ENVELOPE. THE ONLY DIFFERENCE IS IN THE FORWARD SPEED SHOWN BY VARIOUS MODELS...BUT THIS MOSTLY OCCUR AT THE LONG RANGE AS THE SYSTEM BEGINS THE TRANSITION TO AN EXTRATROPICAL LOW. FORECAST POSITIONS AND MAX WINDS INITIAL 07/0300Z 29.1N 66.5W 40 KT 12HR VT 07/1200Z 30.3N 66.1W 40 KT 24HR VT 08/0000Z 32.0N 65.2W 45 KT 36HR VT 08/1200Z 33.7N 64.4W 55 KT 48HR VT 09/0000Z 36.5N 63.0W 55 KT 72HR VT 10/0000Z 42.0N 57.5W 55 KT 96HR VT 11/0000Z 49.5N 46.5W 45 KT...POST-TROP/EXTRATROP 120HR VT 12/0000Z...ABSORBED BY A LARGER EXTRATROPICAL CYCLONE $$ FORECASTER AVILA |
