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| #112306 (Received by flhurricane at: 10:40 PM 21.Sep.2006) TCDAT3 HURRICANE HELENE DISCUSSION NUMBER 39 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 PM EDT THU SEP 21 2006 THE SATELLITE REPRESENTATION OF HELENE HAS IMPROVED SLIGHTLY DURING THE LAST COUPLE OF HOURS...AND COLD CLOUD TOPS HAVE EXPANDED AND BECOME MORE CONCENTRIC AROUND THE CENTER. DVORAK DATA-T NUMBERS HAVE INCREASED TO 4.5 OR 77 KT FOR BOTH TAFB AND AFWA. ACCORDINGLY...THE INITIAL INTENSITY HAS BEEN BUMPED UP TO 75 KT. THE OFFICIAL INTENSITY FORECAST CLOSELY FOLLOWS THE SHIPS GUIDANCE. HELENE IS EXPECTED TO REMAIN OVER 26C TO 27C WATER FOR THE NEXT 24 HOURS OR SO WITH ONLY A MARGINAL INCREASE IN WEST-SOUTHWESTERLY SHEAR. THIS SHOULD KEEP HELENE IN A STEADY STATE FOR THE NEXT DAY. AFTER WHICH...VERY SLOW WEAKENING IS ANTICIPATED AS HELENE TRANSITIONS INTO A POTENTIALLY STRONG EXTRATROPICAL CYCLONE IN ABOUT 2 TO 3 DAYS...AS COLD AIR BECOMES ENTRAINED INTO THE WESTERN SIDE OF THE CYCLONE. THE INITIAL MOTION IS NORTH-NORTHEASTWARD OR 015/12. WATER VAPOR IMAGERY INDICATES A BROAD DEEP-LAYER TROUGH RACING EASTWARD TOWARD HELENE WITH A DRY PUNCH OUT AHEAD OF IT. THIS TROUGH WILL HELP ACCELERATE HELENE TO THE NORTH-NORTHEAST AND NORTHEAST FOR THE NEXT 48 TO 72 HOURS. THE MODEL GUIDANCE IS CONSISTENT WITH THIS SCENARIO...THEN THE MODELS DIVERGE A BIT AT DAYS 4 AND 5 AS HELENE BECOMES EXTRATROPICAL. THE UKMET IS THE GREATEST OUTLIER AND TAKES HELENE TO THE EAST AND EVENTUALLY TO THE SOUTH...AND SHIFTS THE CONSENSUS GUIDANCE TO THE SOUTH AS WELL. THE GFS HAS A MORE NORTHWARD TRACK WHILE THE GFDL...NOGAPS...AND FSU SUPERENSEMBLE TAKE THE CYCLONE TO THE NORTHEAST. THE OFFICIAL FORECAST IS SLIGHTLY SOUTH OF THE PREVIOUS TRACK BUT REMAINS IN CLOSE AGREEMENT WITH GFDL AND FSU SUPERENSEMBLE SOLUTIONS. THE WIND RADII HAVE BEEN ADJUSTED TO REFLECT DATA FROM A 2226 UTC QUIKSCAT PASS. FORECAST POSITIONS AND MAX WINDS INITIAL 22/0300Z 31.8N 56.3W 75 KT 12HR VT 22/1200Z 33.6N 54.8W 75 KT 24HR VT 23/0000Z 36.3N 51.2W 75 KT 36HR VT 23/1200Z 38.9N 45.9W 70 KT 48HR VT 24/0000Z 41.7N 40.0W 65 KT...BECOMING EXTRATROPICAL 72HR VT 25/0000Z 47.0N 30.0W 60 KT...EXTRATROPICAL 96HR VT 26/0000Z 51.5N 23.0W 60 KT...EXTRATROPICAL 120HR VT 27/0000Z 58.0N 17.0W 55 KT...EXTRATROPICAL $$ FORECASTER MAINELLI/BEVEN |
