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| #381347 (Received by flhurricane at: 10:47 AM 06.Oct.2010) TCDAT2 SUBTROPICAL DEPRESSION SEVENTEEN DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172010 1100 AM AST WED OCT 06 2010 DURING THE PAST 6 HOURS...SATELLITE IMAGERY INDICATES THAT DEEP CONVECTION HAS DEVELOPED IN THE NORTHWEST QUADRANT CLOSER TO THE CENTER. HOWEVER...VISIBLE IMAGERY ALSO INDICATES THAT THERE ARE MULTIPLE SMALL SWIRLS ROTATING AROUND THE CENTER OF THE LARGER CYCLONIC GYRE. AS A RESULT...THE INITIAL POSITION IS LOCATED AT THE MEAN CENTER OF THE BROADER CIRCULATION. SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS TROPICAL T2.5/35 KT FROM TAFB AND SAB...AND AN ADT ESTIMATE OF T2.1/31 KT FROM UW-CIMSS. EARLIER AMSU TEMPERATURE DATA ALSO INDICATED THAT A WEAK WARM CORE WAS LOCATED BETWEEN 600-400 MB...SUGGESTING THAT THE SYSTEM WAS NOT FULLY NOT FULLY TROPICAL. GIVEN THAT THIS SYSTEM IS STILL INTERACTING WITH AN UPPER-LEVEL LOW NOTED IN WATER VAPOR IMAGERY TO BE CENTERED JUST SOUTHEAST OF THE LOW-LEVEL CENTER...THE INITIAL INTENSITY WILL BE HELD AT 30 KT AND THE SYSTEM WILL ALSO RETAIN SUBTROPICAL DEPRESSION STATUS FOR THIS ADVISORY. AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT IS SCHEDULED TO INVESTIGATE THE CYCLONE AROUND 18Z...WHICH SHOULD PROVIDE A BETTER INTENSITY ESTIMATE. THE INITIAL MOTION ESTIMATE IS 325/8 BASED ON MICROWAVE POSITIONS AND USING THE AFOREMENTIONED MEAN FIX POSITION DATA. THE CYCLONE IS MOVING NORTHWESTWARD TOWARD A WEAKNESS IN A DEEP-LAYER RIDGE LOCATED TO THE NORTH. A WEAK COLD FRONTAL SYSTEM IS EMBEDDED IN THE WEAKNESS...AND A STRONG MID-TROPOSPHERIC TROUGH LOCATED OVER THE EASTERN U.S. IS FORECAST TO MOVE EASTWARD AND WEAKEN THE RIDGE AND ALSO STRENGTHEN THE FRONT SYSTEM. THE CYCLONE IS EXPECTED TO GRADUALLY MOVE THROUGH THE WEAKNESS AND ACCELERATE AHEAD OF THE TROUGH AFTER 36 HOURS...AND MERGE WITH THE FRONTAL SYSTEM AND BECOME EXTRATROPICAL BY 96 HOURS. THE FORECAST IS A LITTLE TO THE LEFT OF THE PREVIOUS TRACK...MAINLY DUE TO THE MORE WESTWARD INITIAL POSITION...AND IS SIMILAR TO THE CONSENSUS MODEL...TVCN. GRADUAL TRANSITION TO A FULLY TROPICAL LOW PRESSURE SYSTEM IS EXPECTED TO OCCUR WITHIN THE NEXT 12 HOURS NOW THAT DEEP CONVECTION HAS DEVELOPED WITHIN ABOUT 30 NMI OF THE LOW-LEVEL CENTER. HOWEVER...THIS TROPICAL TRANSITION COULD COMPLICATE THE INTENSITY FORECAST SINCE TROPICAL CYCLONE INTENSIFICATION PROCESSES USUALLY OCCUR ON MUCH SHORTER TIME SCALES THAN THOSE ASSOCIATED WITH SUBTROPICAL CYCLONES. THE VERTICAL SHEAR IS FORECAST TO REMAIN RELATIVELY LOW FOR THE NEXT 36-48 HOURS WHILE THE CYCLONE WILL BE OVER WARM SSTS OF GREATER THAN 28C. THIS SHOULD ALLOW FOR AT LEAST SOME MODEST STRENGTHENING TO OCCUR. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF ALL OF THE NHC INTENSITY GUIDANCE. HOWEVER...IT SHOULD BE NOTED THAT THE SHIPS MODEL MAKES THE CYCLONE A HURRICANE BY 72 HOURS...WHICH IS A VIABLE POSSIBILITY IF THE SYSTEM TAKES ON A MORE CLASSICAL TROPICAL CYCLONE STRUCTURE. FORECAST POSITIONS AND MAX WINDS INITIAL 06/1500Z 23.0N 68.0W 30 KT 12HR VT 07/0000Z 23.5N 68.3W 35 KT 24HR VT 07/1200Z 24.2N 68.2W 40 KT 36HR VT 08/0000Z 24.9N 67.2W 45 KT 48HR VT 08/1200Z 26.1N 65.2W 50 KT 72HR VT 09/1200Z 29.3N 58.3W 50 KT 96HR VT 10/1200Z 33.4N 47.4W 40 KT...POST-TROP/EXTRATROP 120HR VT 11/1200Z 38.0N 34.5W 35 KT...POST-TROP/EXTRATROP $$ FORECASTER STEWART |
