000 WTNT41 KNHC 120233 TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 1100 PM AST SAT SEP 11 2010 THE CLOUD PATTERN ASSOCIATED WITH IGOR HAS INCREASED IN ORGANIZATION DURING THE PAST SEVERAL HOURS. A TIGHTLY-COILED BAND...WITH CLOUD TOP TEMPERATURES TO -85C...WRAPS AROUND THE EASTERN SEMICIRCLE INTO A DEVELOPING CENTRAL DENSE OVERCAST. AN EYE FEATURE HAS ALSO BEEN BRIEFLY INTERMITTENT IN CONVENTIONAL SATELLITE IMAGERY...AND A NUMBER OF MICROWAVE PASSES SEVERAL HOURS AGO REVEALED A DISTINCT CONVECTIVE RING SURROUNDING THE CENTER. SUBJECTIVE DVORAK T-NUMBERS AT 0000 UTC WERE A CONSENSUS 4.0 FROM BOTH SATELLITE AGENCIES...AND 3-HOURLY AVERAGED ADT VALUES FROM UW-CIMSS ARE 4.3. THE INITIAL INTENSITY IS RAISED TO 65 KT THIS ADVISORY...MAKING IGOR THE FOURTH HURRICANE OF THE 2010 ATLANTIC HURRICANE SEASON. THE UNDERLYING OCEAN ONLY GETS WARMER ALONG THE FORECAST TRACK OF IGOR...PEAKING AROUND 29C IN ABOUT 3 DAYS. THAT...COMBINED WITH A LIGHT SHEAR ENVIRONMENT...WOULD FAVOR A STRENGTHENING TREND FOR THE NEXT FEW DAYS...AND NEARLY ALL THE INTENSITY GUIDANCE MAKES IGOR A MAJOR HURRICANE BY 72 HOURS. THEREAFTER...WHILE FLUCTUATIONS IN INTENSITY MAY OCCUR...IGOR IS EXPECTED TO MAINTAIN MAJOR HURRICANE STATUS AND BE A LARGE HURRICANE OVER THE CENTRAL NORTH ATLANTIC. IGOR HAS MAINTAINED ROUGHLY THE SAME MOTION...275/15...THOUGH PERHAPS A TAD SLOWER THAN EARLIER. SUBTROPICAL RIDGING NORTH OF THE CYCLONE SHOULD BE THE DOMINANT STEERING FEATURE FOR THE NEXT 2 TO 3 DAYS...CARRYING IGOR ON A GENERAL WESTWARD TRACK. BEYOND THIS TIME...DYNAMICAL MODELS SHOW IGOR SLOWING AND TURNING WEST- NORTHWESTWARD AS IT APPROACHES AND THEN MOVES INTO A SUBSTANTIAL BREAK IN THE SUBTROPICAL RIDGE. AS WAS THE CASE IN THE PREVIOUS MODEL CYCLE...THERE CONTINUES TO BE CONSIDERABLE SPREAD IN THE TRACK GUIDANCE...WITH THE GFDL/HWRF THE RIGHTMOST OF MODEL SOLUTIONS AND THE UKMET/NOGAPS THE LEFTMOST. THESE DIFFERENCES SEEM TO HINGE ON THE STRENGTH AND POSITION OF THE SUBTROPICAL RIDGE...WITH THE FORMER MODELS FORECASTING A WEAKER RIDGE DISPLACED TO THE EAST WHILE LATTER INDICATE A MORE ROBUST RIDGE EXTENDING FARTHER WEST. THE OFFICIAL NHC FORECAST TRACK HAS BEEN ADJUSTED TO THE RIGHT...FOLLOWING THE TREND IN THE GUIDANCE... BUT IS NOT AS FAR RIGHT AS THE MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INITIAL 12/0300Z 17.7N 42.5W 65 KT 12HR VT 12/1200Z 17.8N 44.8W 75 KT 24HR VT 13/0000Z 17.9N 47.4W 80 KT 36HR VT 13/1200Z 18.1N 49.7W 90 KT 48HR VT 14/0000Z 18.4N 51.9W 100 KT 72HR VT 15/0000Z 19.5N 55.0W 110 KT 96HR VT 16/0000Z 21.5N 58.0W 115 KT 120HR VT 17/0000Z 23.5N 61.0W 115 KT $$ FORECASTER KIMBERLAIN