000 WTNT41 KNHC 140246 TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 24 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 1100 PM AST MON SEP 13 2010 MICROWAVE AND GEOSTATIONARY SATELLITE IMAGERY SUGGESTS THAT AN EYEWALL REPLACEMENT CYCLE MAY HAVE BEGUN. TRMM...WINDSAT...AND SSMIS PASSES FROM ABOUT 5-6 HOURS AGO ALL INDICATED THAT A SECONDARY EYEWALL WAS BEGINNING TO FORM...AND MORE RECENTLY CONVECTIVE TOPS AROUND THE EYE HAVE BEEN WARMING. SUBJECTIVE DVORAK FINAL-T ESTIMATES HAD FALLEN TO T6.0 TAFB AND SAB AT 0000 UTC...AND THE LATEST OBJECTIVE ADT ESTIMATE IS T6.0/6.4. BASED ON THESE DATA...THE INITIAL INTENSITY IS LOWERED TO 120 KT. FOLLOWING A CONSENSUS OF THE INTENSITY GUIDANCE...THE OFFICIAL FORECAST KEEPS IGOR AT THIS INTENSITY FOR THE NEXT 24 HOURS OR SO...BUT IT IS POSSIBLE THAT ADDITIONAL WEAKENING COULD OCCUR WHILE THE EYEWALL REPLACEMENT IS IN PROGRESS. SINCE IGOR IS STILL EXPECTED TO BE OVER WARM OCEAN WATERS AND REMAIN IN A LOW SHEAR ENVIRONMENT...THE FORECAST ALLOWS FOR THE POSSIBILITY OF SOME RE-STRENGTHENING BETWEEN 36-48 HOURS...WHICH IS HINTED AT IN THE SHIPS OUTPUT. WEAKENING IS THEN INDICATED DURING DAYS 3 THROUGH 5...BUT IT IS CONSERVATIVE AND STILL LIES JUST ABOVE THE UPPER BOUND OF THE GUIDANCE. IGOR JUST WILL NOT BUDGE VERY MUCH TO THE NORTH AND IS MOVING 275 DEGREES AT 8 KT. THE UKMET MODEL HAS CAPTURED THIS MOTION WELL OVER THE PAST COUPLE OF DAYS AND HAS CONSISTENTLY BEEN LOCATED ON THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE. SINCE THERE IS STILL NO CLEAR EVIDENCE OF THE BEGINNING OF A TURN...THE NHC FORECAST TRACK LIES ALONG THE SOUTHERN PERIPHERY OF THE TRACK GUIDANCE FOR THE FIRST 24 HOURS...ALTHOUGH STILL NOT AS FAR SOUTH AS THE UKMET. A TURN TOWARD THE NORTHWEST IS EXPECTED BY 36 HOURS WHEN IGOR SHOULD HAVE REACHED THE BREAK IN THE SUBTROPICAL RIDGE. THE SPREAD IN THE MODELS FROM DAYS 3 THROUGH 5 HAS AGAIN TIGHTENED...AND THE OFFICIAL FORECAST IS CHANGED LITTLE FROM THE PREVIOUS ONE. THIS FORECAST ALSO LIES CLOSE TO A MULTI-MODEL CONSENSUS THAT EXCLUDES THE GFDN...WHICH HAS BEEN FASTER THAN THE OTHER GUIDANCE FOR SEVERAL CYCLES. 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 14/0300Z 17.7N 51.2W 120 KT 12HR VT 14/1200Z 18.0N 52.3W 120 KT 24HR VT 15/0000Z 18.8N 53.7W 120 KT 36HR VT 15/1200Z 19.9N 55.2W 125 KT 48HR VT 16/0000Z 21.1N 56.6W 125 KT 72HR VT 17/0000Z 24.0N 59.5W 115 KT 96HR VT 18/0000Z 27.0N 62.5W 105 KT 120HR VT 19/0000Z 30.5N 64.5W 95 KT $$ FORECASTER BERG