000 WTNT41 KNHC 172040 TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 39 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 500 PM AST FRI SEP 17 2010 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING IGOR EARLY THIS AFTERNOON MEASURED A MINIMUM PRESSURE OF 946 MB. THE HURRICANE HUNTER ALSO MEASURED MAXIMUM FLIGHT-LEVEL AND SFMR WINDS OF 102 AND 79 KT...RESPECTIVELY. THE INITIAL INTENSITY IS LOWERED TO 90 KT BASED UPON THE AIRCRAFT OBSERVATIONS. DATA FROM THE PLANE ALSO INDICATED A RATHER BROAD WIND FIELD...WITH THE PRESENCE OF A DOUBLE WIND MAXIMA. SINCE THE PLANE DEPARTED...THE CLOUD PATTERN OF IGOR HAS INCREASED IN ORGANIZATION...WITH COLDER CLOUD TOPS DEVELOPING WITHIN THE INNER CORE AND THE EYE BECOMING VISIBLE AGAIN. INNER CORE DYNAMICS NOTWITHSTANDING...THERE APPEARS TO BE A FINAL WINDOW OF OPPORTUNITY FOR RE-INTENSIFICATION DURING THE NEXT DAY OR SO AS IGOR REMAINS IN A LIGHT SHEAR ENVIRONMENT AND MOVES OVER WARM WATERS. AFTER ABOUT 36 HOURS...A GRADUAL INCREASE IN SOUTHERLY AND SOUTHWESTERLY SHEAR AND COOLER WATERS ALONG THE FORECAST TRACK SHOULD PROMOTE A WEAKENING OF IGOR. THE OFFICIAL INTENSITY FORECAST HAS BEEN ADJUSTED DOWNWARD A BIT IN THE SHORT TERM BASED UPON CURRENT TRENDS BUT IS NEARLY THE SAME LATER IN THE PERIOD. IN AGREEMENT WITH THE GUIDANCE...IGOR IS FORECAST TO BECOME A LARGE AND STRONG EXTRATROPICAL CYCLONE OVER THE FAR NORTH ATLANTIC BEYOND 96 HOURS. IGOR APPEARS TO BE ON TRACK...AND THE INITIAL MOTION ESTIMATE IS 305/09. THE TRACK FORECAST PHILOSOPHY HAS NOT CHANGED. IGOR SHOULD BE STEERED NORTHWESTWARD AND THEN NORTH-NORTHWESTWARD AROUND THE WESTERN SIDE OF A SUBTROPICAL RIDGE DURING THE NEXT 36 HOURS. AFTER THAT...A VIGOROUS SHORTWAVE TROUGH MOVING ACROSS THE NORTHEASTERN U.S. SHOULD GRADUALLY TURN THE HURRICANE NORTHWARD IN THE VICINITY OF BERMUDA...AND THEN NORTHEASTWARD WITH A SUBSTANTIAL INCREASE IN FORWARD SPEED. THE OFFICIAL NHC TRACK FORECAST IS VERY CLOSE TO THE PREVIOUS ONE AND REMAINS CLOSE TO THE MULTI-MODEL CONSENSUS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. THE WIND RADII HAVE BEEN EXPANDED BASED UPON DATA FROM THE RECONNAISSANCE AIRCRAFT AND AN EARLIER ASCAT OVERPASS. FORECAST POSITIONS AND MAX WINDS INITIAL 17/2100Z 23.7N 61.1W 90 KT 12HR VT 18/0600Z 24.8N 62.4W 95 KT 24HR VT 18/1800Z 26.2N 64.0W 100 KT 36HR VT 19/0600Z 27.9N 64.9W 95 KT 48HR VT 19/1800Z 30.0N 65.1W 90 KT 72HR VT 20/1800Z 35.5N 62.0W 85 KT 96HR VT 21/1800Z 43.5N 52.5W 75 KT...POST-TROP/EXTRATROP 120HR VT 22/1800Z 52.0N 44.0W 65 KT...POST-TROP/EXTRATROP $$ FORECASTER KIMBERLAIN