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| #377199 (Received by flhurricane at: 4:56 AM 19.Sep.2010) TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 45 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 500 AM AST SUN SEP 19 2010 DATA FROM THE HURRICANE HUNTER AIRCRAFT AND SATELLITE IMAGERY INDICATE THAT IGOR HAS CONTINUED TO SLOWLY WEAKEN. THE AIRCRAFT DID NOT REPORT AN EYEWALL...AND SOME DRY AIR ALSO APPEARS TO BE WORKING ITS WAY INTO THE CIRCULATION...PARTICULARLY OVER THE WESTERN SEMICIRCLE. THE INITIAL INTENSITY IS LOWERED TO 75 KT BASED ON A BLEND OF THE FLIGHT LEVEL MAXIMUM WIND OF 91 KT AND A MAXIMUM SFMR READING OF 68 KT. WHILE THE STRONGEST WINDS HAVE DECREASED...THE SFMR DATA SHOWS THAT THE WIND FIELD OF IGOR CONTINUES TO BROADEN...AND THE 50-KT AND 64-KT WIND RADII HAVE BEEN INCREASED. LITTLE CHANGE IN INTENSITY IS EXPECTED FOR THE NEXT COUPLE OF DAYS...AND IGOR WILL BE A LARGE HURRICANE AS IT PASSES BY BERMUDA IN THE NEXT 24 HOURS AND SUBJECTS THAT ISLAND TO A LONG PERIOD OF STRONG WINDS...WITH TROPICAL STORM CONDITIONS LIKELY LASTING AT LEAST 24 HOURS. BY 72 HOURS...IGOR WILL TRANSITION TO A POWERFUL AND LARGE EXTRATROPICAL CYCLONE AND THEN SLOWLY WEAKEN THROUGH THE END OF THE PERIOD. THE INITIAL MOTION ESTIMATE IS 340/10. THE LATEST AIRCRAFT FIXES WERE LOCATED A LITTLE TO THE WEST OF THE APPARENT CENTER IN GEOSTATIONARY IMAGERY...AND ALSO A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST TRACK. THE OVERALL TRACK FORECAST REASONING REMAINS UNCHANGED...AS IGOR WILL TURN NORTHWARD SOON AS IT MOVES AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE...AND THEN ACCELERATE TOWARD THE NORTHEAST ON MONDAY AS IT RECURVES AHEAD OF A MID-LATITUDE TROUGH MOVING OFF THE COAST OF NORTH AMERICA. THROUGH 36 HOURS THE OFFICIAL FORECAST HAS BEEN ADJUSTED A LITTLE TO THE LEFT OF THE PREVIOUS ONE TO ACCOUNT FOR THE INITIAL POSITION AND LIES ALONG THE EASTERN EDGE OF THE TIGHTLY CLUSTERED GUIDANCE ENVELOPE. THE SPREAD IN THE GUIDANCE INCREASES BEYOND 48 HOURS DUE TO VARIATIONS IN THE DETAILS OF HOW IGOR INTERACTS WITH THE MID-LATITUDE FLOW DURING AND AFTER EXTRATROPICAL TRANSITION. THE OFFICIAL FORECAST HAS BEEN ADJUSTED NORTHWARD AT DAYS 3 AND 4 AND IS IN BEST AGREEMENT WITH THE GFS MODEL. AT DAY 5 THE OFFICIAL FORECAST SHOWS POST-TROPICAL IGOR SLOWING AND TURNING MORE NORTHWARD ...HOWEVER CONFIDENCE IS LOW IN THIS SCENARIO AS THE SPREAD IN THE GUIDANCE IS VERY LARGE. FORECAST POSITIONS AND MAX WINDS INITIAL 19/0900Z 28.9N 65.3W 75 KT 12HR VT 19/1800Z 30.5N 65.5W 75 KT 24HR VT 20/0600Z 33.4N 64.9W 75 KT 36HR VT 20/1800Z 37.0N 62.5W 75 KT 48HR VT 21/0600Z 41.0N 57.5W 75 KT 72HR VT 22/0600Z 49.0N 47.0W 70 KT...POST-TROP/EXTRATROP 96HR VT 23/0600Z 53.0N 38.0W 45 KT...POST-TROP/EXTRATROP 120HR VT 24/0600Z 56.5N 36.5W 35 KT...POST-TROP/EXTRATROP $$ FORECASTER BRENNAN |
