000 WTNT41 KNHC 142059 TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 27 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 500 PM AST TUE SEP 14 2010 CLOUD TOPS SURROUNDING THE EYE HAVE COOLED CONSIDERABLY DURING THE AFTERNOON AND THE EYE HAS ALSO WARMED AND BECOME MORE DISTINCT IN BOTH VISIBLE AND INFRARED SATELLITE IMAGERY. SEVERAL DISTINCT VORTICES INSIDE THE EYE WERE ALSO NOTED...SIMILAR TO WHAT HAS BEEN SEEN WITH PAST HURRICANES THAT WERE NEAR CATEGORY 5 STRENGTH. THE INITIAL INTENSITY IS INCREASED TO 125 KT AND IS SUPPORTED BY SATELLITE INTENSITY ESTIMATES OF T6.5/127 KT FROM SAB...3-HR AVERAGE ODT VALUES OF T6.7/133 KT FROM TAFB...AND UW-CIMSS ADT VALUES OF T6.5/127 KT. THE INITIAL MOTION ESTIMATE IS 295/07...BASED ON A 12-HR AVERAGE OF SMOOTHING OUT THE MANY TROCHOIDAL WOBBLES IN THE TRACK. IGOR MAY BRIEFLY WOBBLE BACK TO THE WEST DURING THE NEXT SEVERAL HOURS...BUT THE GENERAL MOTION OVER THE NEXT 24 HOURS SHOULD BE TOWARD THE WEST-NORTHWEST...FOLLOWED BY A TURN TO THE NORTHWEST AFTER THAT THROUGH 72 HOURS. A SERIES OF SHORTWAVE TROUGHS MOVING QUICKLY IN THE MID-LATITUDE WESTERLIES ACROSS THE NORTHERN U.S. AND THE NORTH ATLANTIC IS FORECAST TO GRADUALLY WEAKEN THE SUBTROPICAL RIDGE BETWEEN 60W-70W LONGITUDE ABOUT EVERY 24-36 HOURS. AS A RESULT... IGOR IS EXPECTED TO TURN NORTHWARD IN 96-120 HOURS AS DEEP-LAYER SOUTHERLY FLOW TO THE EAST OF IGOR STRENGTHENS BETWEEN IT AND A STRONG SUBTROPICAL HIGH FORECAST OT BE NEAR 30N/40W BY THAT TIME. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND IS CLOSE TO THE MIDDLE OF THE TIGHTLY CLUSTERED MODEL GUIDANCE. BY 120 HOURS...IGOR IS EXPECTED TO BE A VERY LARGE HURRICANE AND BE CLOSE ENOUGH TO BERMUDA TO BRING ADVERSE WEATHER CONDITIONS TO THAT ISLAND. IGOR IS FORECAST TO REMAIN IN AN ENVIRONMENT OF LIGHT VERTICAL WIND SHEAR...WARM SEA-SURFACE TEMPERATURES OF NEAR 29C...AND MAINTAIN A VERY FAVORABLE OUTFLOW PATTERN THROUGH THE FORECAST PERIOD. AS A RESULT...THERE MAY BE SOME ADDITIONAL STRENGTHENING DURING THE NEXT 12-24 HOURS...ESPECIALLY LATER TONIGHT DURING THE CONVECTIVE MAXIMUM PERIOD. HOWEVER...OWING TO THE LARGE SIZE OF IGOR...ITS STRONG CATEGORY 4 INTENSITY...AND ITS RELATIVELY SLOW FORWARD MOTION OF LESS THAN 10 KT...SOME COLD UPWELLING MAY OCCUR BENEATH THE CORE OF THE HURRICANE AND CAUSE SOME WEAKENING OF THE CYCLONE DESPITE THE AFOREMENTIONED FAVORABLE CONDITIONS. EYEWALL REPLACEMENT CYCLES ARE ALSO A DISTINCT POSSIBILITY. REGARDLESS... IGOR IS STILL EXPECTED TO REMAIN A MAJOR HURRICANE THROUGH THE FORECAST PERIOD. THE OFFICIAL INTENSITY FORECAST IS A LITTLE HIGHER THAN THE PREVIOUS ADVISORY AND IS SIMILAR TO A BLEND OF THE SHIPS-LGEM INTENSITY MODELS THROUGH 72 HOURS. IT APPEARS AS THOUGH THE SHIPS GUIDANCE AT FOUR AND FIVE DAYS MAY BE ADVERSELY AFFECTED BY THE REPRESENTATION OF THE WARM CORE OF THE HURRICANE IN THE GFS MODEL. IN ADDITION...ALL THE GLOBAL MODELS FORECAST A VERY FAVORABLE OUTFLOW PATTERN THROUGH DAY FIVE...AND SO THE OFFICIAL FORECAST IS HELD A LITTLE ABOVE THE GUIDANCE NEAR THE END OF THE FORECAST PERIOD. FORECAST POSITIONS AND MAX WINDS INITIAL 14/2100Z 18.8N 53.1W 125 KT 12HR VT 15/0600Z 19.5N 54.3W 130 KT 24HR VT 15/1800Z 20.5N 55.6W 125 KT 36HR VT 16/0600Z 21.5N 57.2W 125 KT 48HR VT 16/1800Z 22.6N 58.8W 120 KT 72HR VT 17/1800Z 25.4N 62.1W 115 KT 96HR VT 18/1800Z 28.6N 64.5W 110 KT 120HR VT 19/1800Z 33.0N 65.5W 100 KT $$ FORECASTER STEWART