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| #375841 (Received by flhurricane at: 4:40 PM 13.Sep.2010) TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 23 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 500 PM AST MON SEP 13 2010 THE STRUCTURE OF IGOR HAS CHANGED LITTLE OVER THE PAST FEW HOURS. THE EYE REMAINS VERY DISTINCT IN IR AND VISIBLE IMAGERY...AND ALTHOUGH THE TOPS SURROUNDING THE EYE HAVE WARMED A BIT...DVORAK CLASSIFICATIONS STILL SUPPORT AN INTENSITY OF 130 KT. IGOR WILL REMAIN IN A FAVORABLE ENVIRONMENT FOR MAINTAINING ITS CURRENT INTENSITY FOR THE NEXT COUPLE OF DAYS...AND THE OFFICIAL FORECAST DOES NOT SHOW ANY WEAKENING UNTIL AFTER 48 HOURS. WHILE A 1640 UTC AMSR-E PASS DOES NOT SHOW ANY EVIDENCE OF A SECONDARY EYEWALL YET...IT IS POSSIBLE THAT AN EYEWALL REPLACEMENT CYCLE WILL OCCUR IN THE FIRST COUPLE OF DAYS...WHICH COULD RESULT IN SOME INTENSITY FLUCTUATIONS NOT REPRESENTED IN THE OFFICIAL FORECAST. BEYOND 36 HOURS...ALL OF THE INTENSITY GUIDANCE SUGGEST THAT SLOW WEAKENING SHOULD BEGIN...ALTHOUGH THERE ARE NO OVERLY NEGATIVE FACTORS UNTIL THE VERY END OF THE PERIOD WHEN THE VERTICAL SHEAR MAY INCREASE. THE OFFICIAL FORECAST SHOWS A GRADUAL WEAKENING AT DAYS 3 THROUGH 5 BUT IS HIGHER THAN MOST OF THE GUIDANCE THROUGH THE PERIOD. THE INITIAL MOTION IS STILL DUE WEST...270 DEGREES...AT 9 KNOTS. ALL OF THE GUIDANCE...EXCEPT THE UKMET...INSISTS ON A TURN TOWARD THE WEST-NORTHWEST IN THE NEXT 12 HOURS AS IGOR BEGINS TO MOVE INTO A LARGE WEAKNESS IN THE SUBTROPICAL RIDGE. HOWEVER...DUE TO THE INITIAL POSITION AND MOTION...THE OFFICIAL FORECAST HAS AGAIN BEEN ADJUSTED A LITTLE TO THE LEFT OF THE PREVIOUS ADVISORY THROUGH 48 HOURS. BEYOND THAT TIME...THERE IS STILL SOME SPREAD IN THE TRACK GUIDANCE. THE ECMWF AND UKMET STILL SHOW A STRONGER RIDGE NORTH OF IGOR THROUGH MUCH OF THE PERIOD...TAKING THE CYCLONE FARTHER WEST THAN THE REST OF THE GUIDANCE. THE GFS AND GFDL CONTINUE TO SHOW THE LEAST RIDGING AND TURN IGOR NORTH-NORTHWESTWARD AT THE END OF THE PERIOD AHEAD OF A MID-LATITUDE TROUGH. WHILE CONFIDENCE IN THE TRACK FORECAST LATE IN THE PERIOD REMAINS LOW...THE GUIDANCE SHOWS A LITTLE LESS SPREAD NOW THAN EARLIER TODAY. THE NEW OFFICIAL FORECAST SHOWS A NORTHWESTWARD MOTION AT DAYS 3 THROUGH 5...AND IS SIMILAR TO THE PREVIOUS FORECAST. THIS ENDS UP BEING VERY CLOSE TO THE TVCN MULTI-MODEL CONSENSUS AND A BLEND OF THE GFS AND ECMWF MODELS. LARGE SWELLS FROM IGOR WILL BEGIN AFFECTING THE LEEWARD ISLANDS TOMORROW AND REACH PUERTO RICO AND THE VIRGIN ISLANDS BY WEDNESDAY. FORECAST POSITIONS AND MAX WINDS INITIAL 13/2100Z 17.7N 50.5W 130 KT 12HR VT 14/0600Z 18.1N 51.7W 130 KT 24HR VT 14/1800Z 18.9N 53.2W 130 KT 36HR VT 15/0600Z 20.0N 54.7W 130 KT 48HR VT 15/1800Z 21.1N 56.1W 130 KT 72HR VT 16/1800Z 23.5N 58.5W 120 KT 96HR VT 17/1800Z 26.5N 61.5W 110 KT 120HR VT 18/1800Z 30.0N 64.0W 105 KT $$ FORECASTER BRENNAN |
