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| #377009 (Received by flhurricane at: 10:50 AM 18.Sep.2010) TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 42 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 1100 AM AST SAT SEP 18 2010 THERE HAS BEEN LITTLE CHANGE IN THE STRUCTURE OF IGOR DURING THE PAST SEVERAL HOURS. RECENT MICROWAVE OVERPASSES SUGGEST THE HURRICANE IS UNDERGOING AN EYEWALL REPLACEMENT CYCLE...WITH THE 20 NM WIDE INNER EYE SEEN IN THE PREVIOUS AIRCRAFT MISSION GRADUALLY WEAKENING. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN 102 KT...AND THE INITIAL INTENSITY REMAINS 95 KT. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS CURRENTLY EN ROUTE TO INVESTIGATE IGOR. THE INITIAL MOTION IS 310/10. DURING THE NEXT 36-72 HR...IGOR WILL ROUND THE WESTERN END OF A DEEP-LAYER RIDGE OVER THE CENTRAL AND EASTERN ATLANTIC AND ENTER THE WESTERLIES TO THE EAST OF A SHORTWAVE TROUGH MOVING OFF THE COAST OF EASTERN NORTH AMERICA. THE TRACK GUIDANCE IS IN GOOD AGREEMENT WITH THIS SCENARIO AND HAS CHANGED LITTLE SINCE THE PREVIOUS ADVISORY. THIS PART OF THE THE NEW FORECAST TRACK IS THUS AN UPDATE OF THE PREVIOUS ONE...WITH THE CENTER OF IGOR PASSING NEAR OR OVER BERMUDA IN 36-48 HR. AFTER 72 HR...THERE IS SOME SPREAD IN THE GUIDANCE AS IGOR UNDERGOES EXTRATROPICAL TRANSITION. THE ECMWF TURNS THE CYCLONE SHARPLY TO THE NORTH...WHILE THE OTHER DYNAMICAL MODELS SHOW A MORE NORTHEASTWARD TO EASTWARD MOTION. THIS PART OF THE TRACK IS SHIFTED TO THE EAST OF THE PREVIOUS FORECAST BASED ON A BLEND OF THE DYNAMICAL MODELS...BUT LIES TO THE NORTH OF THE CENTER OF THE GUIDANCE ENVELOPE. IGOR IS IN AN ENVIRONMENT OF LIGHT SOUTHERLY VERTICAL SHEAR...AND THIS IS FORECAST TO CONTINUE FOR THE NEXT 24 HR OR SO. AFTER THAT...THE HURRICANE IS FORECAST TO ENCOUNTER INCREASING SHEAR. IT IS UNCERTAIN IF THE CURRENT EYEWALL REPLACEMENT CYCLE WILL BE COMPLETE ENOUGH TO ALLOW STRENGTHENING BEFORE THE SHEAR INCREASES...BUT CURRENT TRENDS SUGGEST IT WILL NOT. MOST OF THE INTENSITY GUIDANCE NOW SHOWS LITTLE CHANGE IN STRENGTH OR SLOW WEAKENING DURING THE FIRST 36 HR...WITH ONLY THE SHIPS MODEL SHOWING MODEST STRENGTHENING. THE NEW INTENSITY FORECAST CALLS FOR IGOR TO MAINTAIN A 95 KT INTENSITY FOR 36 HR OR SO...FOLLOWED BY WEAKENING DUE TO SHEAR. IT CANNOT BE RULED OUT THAT IGOR COULD REGAIN MAJOR HURRICANE STATUS BEFORE REACHING BERMUDA...BUT IT APPEARS LESS LIKELY THAN PREVIOUSLY THOUGHT. EXTRATROPICAL TRANSITION SHOULD BE UNDERWAY BY 72 HR AND BE COMPLETE BY 96 HR. IGOR IS EXPECTED TO REMAIN A LARGE AND POWERFUL CYCLONE AFTER EXTRATROPICAL TRANSITION. IGOR CONTINUES TO HAVE A VERY LARGE WIND FIELD...AND CONDITIONS WILL BEGIN TO DETERIORATE ON BERMUDA BY TONIGHT WELL IN ADVANCE OF THE CENTER. FORECAST POSITIONS AND MAX WINDS INITIAL 18/1500Z 26.0N 63.6W 95 KT 12HR VT 19/0000Z 27.1N 64.6W 95 KT 24HR VT 19/1200Z 28.9N 65.3W 95 KT 36HR VT 20/0000Z 31.1N 65.2W 95 KT 48HR VT 20/1200Z 33.9N 64.2W 90 KT 72HR VT 21/1200Z 40.5N 56.0W 75 KT 96HR VT 22/1200Z 47.5N 44.0W 65 KT...POST-TROP/EXTRATROP 120HR VT 23/1200Z 50.0N 36.5W 50 KT...POST-TROP/EXTRATROP $$ FORECASTER BEVEN |
