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| #111474 (Received by flhurricane at: 10:39 PM 17.Sep.2006) TCDAT3 HURRICANE HELENE DISCUSSION NUMBER 23 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 PM EDT SUN SEP 17 2006 THE HURRICANE IS LOOKING STRONGER THIS EVENING WITH THE RING OF EYEWALL CONVECTION COOLING AROUND THE WARM EYE. IN ADDITION... THE INNER CORE IS MORE SYMMETRIC THAN A FEW HOURS AGO WITH CIRRUS OUTFLOW EXPANDING IN ALL DIRECTIONS... ESPECIALLY TO THE EAST. SUBJECTIVE AND OBJECTIVE DVORAK ESTIMATES SUGGEST THAT HELENE IS A MAJOR HURRICANE AND THE INITIAL INTENSITY HAS BEEN CONSERVATIVELY INCREASED TO 100 KT... MAKING HELENE THE SECOND MAJOR HURRICANE OF THE SEASON. THERE ARE NO OBVIOUS HINDRANCES TO FUTURE INTENSIFICATION OVER THE NEXT COUPLE OF DAYS AS HELENE MOVES OVER PROGRESSIVELY WARMER WATERS AND STAYS IN A RELATIVELY LIGHT SHEAR ENVIRONMENT. CURIOUSLY... THE SHIPS/GFDL DO NOT SHOW MUCH FURTHER STRENGTHENING IN AN ENVIRONMENT THAT IS SEEMINGLY FAVORABLE FOR MORE INTENSIFICATION. THE OFFICIAL WIND SPEED FORECAST IS A LITTLE HIGHER THAN SHIPS/GFDL AND CLOSE TO THE FSU SUPERENSEMBLE. A SLOW WEAKENING COULD COMMENCE IN A COUPLE OF DAYS AS SOME MODELS HINT AT AN INCREASE IN SHEAR. HOWEVER THE LARGE SPREAD OF THE TRACK MODELS IN THE EXTENDED PERIOD MAKES FOR A MORE UNCERTAIN INTENSITY FORECAST THAN USUAL AT 3-5 DAYS. THE INITIAL MOTION IS A LITTLE SLOWER THAN PREVIOUSLY ESTIMATED... ABOUT 315/7. GLOBAL MODELS ARE IN GOOD AGREEMENT ON THIS GENERAL MOTION CONTINUING FOR ABOUT 24 HOURS FOLLOWED BY A TURN TOWARD THE WEST OR WEST-NORTHWEST AS RIDGING REBUILDS IN BETWEEN GORDON AND HELENE. THEREAFTER... THE BIG PROBLEM IS IF A TROUGH... NOW CURRENTLY JUST OFFSHORE OF THE UNITED STATES... WEAKENS THE RIDGE ENOUGH TO ALLOW THE HURRICANE TO BE PICKED UP BY A SECOND TROUGH IN A FEW DAYS. MODEL GUIDANCE IS GENERALLY SPLIT INTO TWO CLUSTERS. THE GFS/UKMET/NOGAPS SUGGEST THAT THE TROUGH WILL LEAVE THE HURRICANE BEHIND WHILE THE ECMWF/GFDL BELIEVE THE TROUGH WILL ACCELERATE THE HURRICANE OUT TO SEA. MODEL GUIDANCE HAS BEEN TRENDING WESTWARD WITH TIME... AND THE OFFICIAL FORECAST LEANS TOWARD THE WESTWARD CLUSTER OF GFS/UKMET/NOGAPS. FORECAST POSITIONS AND MAX WINDS INITIAL 18/0300Z 21.6N 49.4W 100 KT 12HR VT 18/1200Z 22.3N 50.2W 105 KT 24HR VT 19/0000Z 23.0N 51.5W 110 KT 36HR VT 19/1200Z 23.3N 53.1W 110 KT 48HR VT 20/0000Z 23.6N 54.8W 110 KT 72HR VT 21/0000Z 25.0N 58.0W 100 KT 96HR VT 22/0000Z 27.5N 59.5W 95 KT 120HR VT 23/0000Z 29.5N 61.5W 90 KT $$ FORECASTER BLAKE/PASCH |
