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| #376444 (Received by flhurricane at: 10:47 AM 16.Sep.2010) TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 34 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 1100 AM AST THU SEP 16 2010 IGOR IS MAINTAINING VERY DEEP CONVECTION AND A 30-35 NMI WIDE EYE WITHIN A CENTRAL DENSE OVERCAST...BUT THE OVERALL CONVECTIVE PATTERN HAS BECOME MORE ASYMMETRIC. THE RESTRICTED NATURE OF THE OUTFLOW TO THE WEST OF THE CYCLONE SUGGESTS SOME UPPER-LEVEL WESTERLY FLOW IMPINGING ON THE CIRCULATION...WHICH MAY ALSO BE CONTRIBUTING TO THE RAGGED APPEARANCE OF THE CDO. SUBJECTIVE DVORAK T-NUMBERS ARE A CONSENSUS 6.0 AT 1200 UTC AND SERVE AS THE BASIS FOR LOWERING THE INTENSITY TO 115 KT FOR THIS ADVISORY. AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT IS SCHEDULED TO INVESTIGATE IGOR IN A FEW HOURS AND WILL PROVIDE A MORE ACCURATE ASSESSMENT OF ITS INTENSITY. WATER VAPOR IMAGERY SUGGESTS THAT THE COMBINATION OF A SHEAR AXIS NORTHWEST OF IGOR AND THE SOUTHWESTWARD DISPLACEMENT OF THE UPPER-LEVEL ANTICYCLONE ASSOCIATED WITH IGOR MAY BE IMPARTING WEAK TO MODERATE WESTERLY SHEAR TO THE HURRICANE. SHIPS MODEL OUTPUT INDICATES THAT THIS SHEAR MAY PERSIST FOR NEXT 12-24 HOURS AND THEN DECREASE...ALLOWING FOR SOME INTENSIFICATION BEFORE ABOUT 48 HOURS. ALTHOUGH INNER CORE DYNAMICS WILL LIKELY INDUCE SOME DIFFICULT TO PREDICT FLUCTUATIONS IN INTENSITY...IGOR IS EXPECTED TO REMAIN A LARGE AND FORMIDABLE HURRICANE FOR THE NEXT 3 TO 4 DAYS. AFTER THAT...INCREASING SOUTHWESTERLY SHEAR AND GRADUALLY COOLER WATERS SHOULD LEAD TO WEAKENING OF THE CYCLONE...WITH THE WEAKENING POSSIBLY GREATER THAN INDICATED IF THE 30 TO 45 KT OF SHEAR PREDICTED BY THE GFS VERIFIES. THE GUIDANCE ALSO INDICATES THAT EXTRATROPICAL TRANSITION WILL BE UNDERWAY BY DAY 5. THE OFFICIAL FORECAST IS SLIGHTLY HIGHER THAN SOME OF THE STATISTICAL-DYNAMICAL GUIDANCE BUT SIMILAR TO THE PREVIOUS INTENSITY FORECAST. IGOR HAS BEEN WOBBLING ABOUT AN INITIAL MOTION OF 305/06. LITTLE HAS CHANGED REGARDING THE OVERALL TRACK PHILOSOPHY. THE HURRICANE IS EXPECTED TO MOVE NORTHWESTWARD AROUND THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE DURING THE NEXT 72 HOURS. BEYOND 72 HOURS...IGOR SHOULD BECOME EMBEDDED WITHIN THE MID-LATITUDE WEST-SOUTHWESTERLY FLOW AHEAD OF A VIGOROUS SHORTWAVE TROUGH MOVING THROUGH THE NORTHEASTERN U.S. AND THE CANADIAN MARITIMES...AND TURN NORTH AND THEN NORTHEAST WITH INCREASING FORWARD SPEED. THE SPREAD IN THE MODEL GUIDANCE HAS DECREASED SINCE YESTERDAY...WITH THE LATEST SOLUTIONS TRENDING SLIGHTLY LEFTWARD AND TIGHTLY CLUSTERED AROUND THE OFFICIAL FORECAST. FORECAST POSITIONS AND MAX WINDS INITIAL 16/1500Z 21.0N 57.2W 120 KT 12HR VT 17/0000Z 21.5N 58.3W 115 KT 24HR VT 17/1200Z 22.4N 60.0W 120 KT 36HR VT 18/0000Z 23.8N 61.7W 120 KT 48HR VT 18/1200Z 25.3N 63.2W 120 KT 72HR VT 19/1200Z 29.0N 65.0W 105 KT 96HR VT 20/1200Z 33.5N 63.5W 95 KT 120HR VT 21/1200Z 39.0N 56.5W 80 KT $$ FORECASTER KIMBERLAIN |
