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| #375686 (Received by flhurricane at: 10:52 PM 12.Sep.2010) TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 20 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 1100 PM AST SUN SEP 12 2010 IGOR HAS CONTINUED TO INTENSIFY WITH VERY COLD CLOUD TOPS...LOWER THAN -70C...WRAPPING AROUND THE SLOWLY-SHRINKING EYE DURING THE PAST SEVERAL HOURS. ALTHOUGH THE TOPS HAVE RECENTLY WARMED A LITTLE OVER THE SOUTHWEST QUADRANT...SUBJECTIVE DVORAK ESTIMATES FROM TAFB AND SAB ARE T6.5/127 KT AND OBJECTIVE ESTIMATES FROM THE ADT AND HIE ALGORITHMS ARE T6.6/130 KT AND T6.9/137 KT... RESPECTIVELY. AS A COMPROMISE...THE INITIAL INTENSITY IS SET AT 130 KT. AN EXPERIMENTAL PRODUCT FROM UW-CIMSS RUN AT NHC INDICATES THAT THERE IS A 42 PERCENT CHANCE OF SECONDARY EYEWALL FORMATION WITHIN THE NEXT 12 HOURS...AND A 90 PERCENT CHANCE WITHIN 24 HOURS. THE PERIOD OF RAPID INTENSIFICATION IS LIKELY TO END SOON...BUT THE OFFICIAL FORECAST FOLLOWS THE SHIPS/LGEM MODELS BY SHOWING IGOR REACHING THE THRESHOLD OF CATEGORY 5 STRENGTH BEFORE THAT HAPPENS. SOME WEAKENING IS THEN INDICATED AFTER EYEWALL REPLACEMENT OCCURS...BUT IGOR IS EXPECTED TO REMAIN A POWERFUL HURRICANE FOR SEVERAL DAYS. AS IS ALWAYS THE CASE WITH STRONG HURRICANES LIKE IGOR...FLUCTUATIONS IN INTENSITY ARE LIKELY BUT ARE ALSO DIFFICULT TO FORECAST. THE MEAN MOTION IS 270/11...BUT IGOR HAS BEEN WOBBLING A LITTLE TO THE SOUTH OF THAT VECTOR. IGOR IS MOVING INTO AN ENVIRONMENT WHERE THE STEERING FLOW IS BECOMING INCREASINGLY DICTATED BY A LARGE LONGWAVE TROUGH OVER THE WESTERN ATLANTIC...AND THE HURRICANE IS EXPECTED TO RESPOND BY TURNING TOWARD THE WEST-NORTHWEST WITHIN THE NEXT 24-48 HOURS. SOME OF THE GLOBAL MODELS INDICATE THAT THE TROUGH COULD FLATTEN A LITTLE BY DAY 3 AND ALLOW THE SUBTROPICAL RIDGE TO BUILD WESTWARD...BUT AT THIS TIME THERE IS TOO MUCH DISAGREEMENT TO INDICATE A WESTWARD TURN IN THE FORECAST. THE TRACK GUIDANCE HAS SHIFTED A LITTLE TO THE NORTH...BUT THE NEW OFFICIAL FORECAST STILL LIES ON THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE UNTIL IT BECOMES CLEAR THAT IGOR IS READY TO TURN. THIS SOLUTION ALSO GIVES CREDENCE TO THE MORE SOUTHERN ECMWF AND UKMET MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 13/0300Z 17.6N 47.8W 130 KT 12HR VT 13/1200Z 17.8N 49.5W 140 KT 24HR VT 14/0000Z 18.2N 51.3W 135 KT 36HR VT 14/1200Z 18.9N 53.0W 130 KT 48HR VT 15/0000Z 19.8N 54.6W 125 KT 72HR VT 16/0000Z 22.0N 57.5W 125 KT 96HR VT 17/0000Z 24.0N 60.0W 120 KT 120HR VT 18/0000Z 27.0N 63.0W 110 KT $$ FORECASTER BERG |
