ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE HELENE DISCUSSION NUMBER 25 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 AM EDT MON SEP 18 2006 HELENE AND GORDON WERE BASICALLY AT THE SAME LONGITUDE THIS MORNING AND THERE WAS A WEAKENING ON THE RIDGE NORTH OF HELENE. THIS RESULTED IN HELENE MOVING IN A NORTH-NORTHWESTWARD TRACK FOR THE PAST SEVERAL HOURS. HOWEVER...IT APPEARS THAT THE HURRICANE IS READY TO BEGIN THE WESTWARD TURN ANTICIPATED BY THE GLOBAL MODELS. IN FACT...HELENE HAS ALREADY TURNED A LITTLE BIT AND IS NOW MOVING TOWARD THE NORTHWEST OR 310 DEGREES AT 8 KNOTS. THE TROUGH CURRENTLY LOCATED OVER THE WESTERN ATLANTIC IS FORECAST TO WEAKEN WHILE A RIDGE TO THE NORTH OF HELENE IS EXPECTED TO AMPLIFY. THIS PATTERN WOULD TEMPORARILY STEER HELENE ON A WESTWARD TRACK FOR A COUPLE OF DAYS. THEREAFTER...GLOBAL MODELS SHOW ANOTHER LARGE TROUGH APPROACHING THE EASTERN UNITED STATES. THIS TROUGH WILL FORCE HELENE SLOWLY NORTHWARD. ALTHOUGH...THE CONFIDENCE IS QUITE HIGH THAT HELENE WILL EVENTUALLY TURN NORTHWARD...IT IS VERY DIFFICULT TO FORECAST THE LONGITUDE THIS WILL OCCUR. THERE ARE SOME INDICATIONS FROM THE LAST RUN OF THE GLOBAL MODELS THAT BY DAYS 4 AND 5...THE STEERING CURRENTS WILL WEAKEN AND HELENE WILL BE MOVING VERY SLOWLY. THERE HAS NO SIGNIFICANT CHANGE IN THE CLOUD PATTERN...JUST A SMALL INCREASE IN THE DVORAK T-NUMBERS. THEREFORE...THE INTENSITY HAS BEEN ADJUSTED UPWARD TO 110 KNOTS. A NOAA P3 PLANE AND NOAA G4 JET...CURRENTLY ON A RESEARCH MISSION IN THE AREA WILL BE PROVIDING VALUABLE DATA THIS AFTERNOON AND WE COULD HAVE A BETTER ESTIMATE OF THE STRUCTURE OF THE HURRICANE AND THE STEERING. HELENE COULD STRENGTHEN JUST LITTLE BIT MORE SINCE THE SHEAR IS LOW AND THE OCEAN IS WARM. HOWEVER...MOST OF THE INTENSITY GUIDANCE FORECAST LITTLE CHANGE OR GRADUAL WEAKENING. FORECAST POSITIONS AND MAX WINDS INITIAL 18/1500Z 23.2N 50.2W 110 KT 12HR VT 19/0000Z 23.9N 51.0W 110 KT 24HR VT 19/1200Z 24.3N 52.8W 115 KT 36HR VT 20/0000Z 24.3N 54.5W 115 KT 48HR VT 20/1200Z 24.5N 56.0W 110 KT 72HR VT 21/1200Z 27.0N 58.0W 105 KT 96HR VT 22/1200Z 29.5N 59.5W 100 KT 120HR VT 23/1200Z 31.5N 60.5W 95 KT $$ FORECASTER AVILA NNNN
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Page last modified: Monday, 18-Sep-2006 14:40:02 UTC