000 WTNT41 KNHC 162041 TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 35 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 500 PM AST THU SEP 16 2010 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT REACHED THE CENTER OF IGOR AROUND 1600 UTC. THE HURRICANE HUNTERS MEASURED A MINIMUM PRESSURE OF 940 MB AND MAXIMUM FLIGHT-LEVEL AND SFMR WINDS OF 130 AND 98 KT...RESPECTIVELY. SINCE THAT TIME..THE CLOUD PATTERN ASSOCIATED WITH IGOR HAS CHANGED LITTLE IN ORGANIZATION...AND DVORAK T-NUMBERS REMAIN AT 5.5 FROM SAB AND TAFB. BASED UPON THE AIRCRAFT DATA AND THE LOWER SATELLITE INTENSITY ESTIMATES...THE INITIAL INTENSITY IS REDUCED TO 110 KT. THE EXTENSION OF AN UPPER-LEVEL TROUGH PASSING NORTH OF IGOR IS STILL PRODUCING ABOUT 15 KT OF WESTERLY SHEAR OVER THE CYCLONE...ACCORDING TO THE LATEST UW-CIMSS ANALYSES. THE SHIPS MODEL OUTPUT SHOWS A REDUCTION IN THE SHEAR WITHIN THE NEXT 12 HOURS AS THIS FEATURE MOVES AWAY...WHICH COULD ALLOW AN OPPORTUNITY FOR SOME RE-INTENSIFICATION IN THE SHORT-TERM. THE GUIDANCE INDICATES THAT IGOR WILL BE MOVING INTO AN ENVIRONMENT OF GRADUALLY INCREASING SOUTHERLY TO SOUTH- SOUTHWESTERLY SHEAR IN ABOUT TWO DAYS...AND OVER COOLER WATERS BY THE END OF THE FORECAST PERIOD. THE COMBINATION OF THESE TWO FACTORS SHOULD RESULT IN A SLOW WEAKENING BEYOND 48 HOURS...AND THE NHC OFFICIAL FORECAST REFLECTS THIS. BY DAY 5...GLOBAL MODELS INDICATE THAT IGOR WILL BE AT LEAST BEGINNING TO UNDERGO EXTRATROPICAL TRANSITION. IGOR CONTINUES TO MAINTAIN ABOUT THE SAME MOTION...310/7. THE REASONING FOR THE TRACK FORECAST IS UNCHANGED. THE HURRICANE IS FORECAST TO MOVE NORTHWESTWARD AND THEN NORTH-NORTHWESTWARD WITH SOME INCREASE IN FORWARD SPEED AROUND THE WESTERN EXTENT OF A SUBTROPICAL RIDGE DURING THE NEXT 48-72 HOURS. BEYOND 72 HOURS... IGOR SHOULD BEGIN ACCELERATING WHILE TURNING NORTH AND THEN NORTHEAST AHEAD OF AN APPROACHING MID-LATITUDE SHORTWAVE TROUGH MOVING THROUGH THE NORTHEAST U.S. AND CANADIAN MARITIMES. THE LATEST MODEL GUIDANCE HAS SHIFTED TO THE LEFT THIS CYCLE APPARENTLY DUE TO TIMING DIFFERENCES ASSOCIATED WITH THE AFORMENTIONED SHORTWAVE TROUGH. THE OFFICIAL NHC TRACK FORECAST HAS BEEN NUDGED WESTWARD...FOLLOWING THE MULTI-MODEL CONSENSUS...AND LIES IN THE MIDDLE OF THE GUIDANCE ENVELOPE. FORECAST POSITIONS AND MAX WINDS INITIAL 16/2100Z 21.7N 58.1W 110 KT 12HR VT 17/0600Z 22.4N 59.2W 110 KT 24HR VT 17/1800Z 23.5N 61.0W 115 KT 36HR VT 18/0600Z 24.9N 62.7W 115 KT 48HR VT 18/1800Z 26.5N 64.0W 110 KT 72HR VT 19/1800Z 30.5N 65.5W 100 KT 96HR VT 20/1800Z 35.5N 62.5W 90 KT 120HR VT 21/1800Z 42.0N 53.0W 70 KT $$ FORECASTER KIMBERLAIN