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| #377073 (Received by flhurricane at: 4:44 PM 18.Sep.2010) TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 43 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 500 PM AST SAT SEP 18 2010 IGOR CONTINUES WORKING ITS WAY THROUGH AN EYEWALL REPLACEMENT CYCLE. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING IGOR FOUND A FRAGMENT OF THE INNER EYEWALL REMAINING INSIDE AN 85 N MI WIDE OUTER EYEWALL. THE CENTRAL PRESSURE WAS 945 MB. THE MAXIMUM 700-MB FLIGHT-LEVEL WINDS WERE 113 KT...WHILE THE MAXIMUM ESTIMATED SURFACE WINDS FROM THE SFMR WERE 73 KT. SURFACE WIND ESTIMATES FROM TWO EYEWALL DROPSONDES WERE NEAR 70 KT AND CONSISTENT WITH THE COINCIDENT SFMR READINGS. BASED ON THESE DATA...THE INITIAL INTENSITY IS REDUCED TO 85 KT...AND IT IS POSSIBLE THAT THIS IS A LITTLE GENEROUS. THE INITIAL MOTION IS 320/12. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY...AND ONLY MINOR TWEAKS TO THE FORECAST TRACK FROM THE PREVIOUS ADVISORY. 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 REMAINS IN GOOD AGREEMENT WITH THIS SCENARIO...WITH THE CENTER OF IGOR PASSING NEAR OR OVER BERMUDA IN ABOUT 36 HR. AFTER 72 HR... THERE REMAINS SPREAD IN THE GUIDANCE AS IGOR UNDERGOES EXTRATROPICAL TRANSITION. THIS PART OF THE TRACK IS SHIFTED A LITTLE TO THE EAST OF THE PREVIOUS FORECAST BASED ON A BLEND OF THE DYNAMICAL MODELS...AND IT NOW LIES NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. IT APPEARS UNLIKELY THAT IGOR WILL COMPLETE THE EYEWALL REPLACEMENT CYCLE IN TIME TO SIGNIFICANTLY STRENGTHEN GIVEN THE CURRENT INTERNAL TRENDS AND THE EXPECTATION OF INCREASED VERTICAL WIND SHEAR AFTER 24 HR. NONE OF THE GUIDANCE SHOWS SIGNIFICANT STRENGTHENING...AND THE NEW INTENSITY FORECAST NOW CALLS FOR LITTLE CHANGE IN STRENGTH DURING THE NEXT 36 HR. AFTER THAT...IGOR SHOULD WEAKEN DUE TO INCREASING SHEAR. 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...AND THIS IS REFLECTED IN THE 96-120 HR INTENSITY FORECAST. IGOR CONTINUES TO HAVE A VERY LARGE WIND FIELD...AND CONDITIONS WILL BEGIN TO DETERIORATE ON BERMUDA TONIGHT WELL IN ADVANCE OF THE CENTER. FORECAST POSITIONS AND MAX WINDS INITIAL 18/2100Z 27.1N 64.3W 85 KT 12HR VT 19/0600Z 28.4N 65.0W 85 KT 24HR VT 19/1800Z 30.5N 65.4W 85 KT 36HR VT 20/0600Z 33.1N 64.9W 85 KT 48HR VT 20/1800Z 36.1N 62.6W 80 KT 72HR VT 21/1800Z 42.5N 52.5W 75 KT 96HR VT 22/1800Z 48.0N 42.0W 75 KT...POST-TROP/EXTRATROP 120HR VT 23/1800Z 50.0N 35.0W 60 KT...POST-TROP/EXTRATROP $$ FORECASTER BEVEN |
