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| #112469 (Received by flhurricane at: 10:34 PM 22.Sep.2006) TCDAT3 TROPICAL STORM HELENE DISCUSSION NUMBER 43 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 PM EDT FRI SEP 22 2006 HELENE IS LOOKING SOMEWHAT LESS TROPICAL IN SATELLITE IMAGERY THIS EVENING. ONLY LIMITED DEEP CONVECTION REMAINS NEAR THE CENTER... WITH THE BULK OF THE COLDER TOPS NOW WELL TO THE NORTH AND NORTHWEST OF THE CENTER. SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM TAFB...55 KT FROM AFWA...AND EXTRATROPICAL FROM SAB. QUIKSCAT DATA FROM 22Z SHOWED 50-60 KT WINDS SOUTHEAST OF THE CENTER...WITH ONE QUESTIONABLE-LOOKING 65 KT VECTOR IN THE SOUTHWEST QUADRANT. BASED ON THE AVAILABLE DATA...HELENE IS DOWNGRADED TO A 60-KT TROPICAL STORM. THE INITIAL AND FORECAST WIND RADII HAVE BEEN EXPANDED CONSIDERABLY BASED ON THE QUIKSCAT DATA. HELENE TURNED TO THE RIGHT BETWEEN 18Z AND 00Z...BUT SINCE THEN LOOKS LIKE IT MAY BE TURNING BACK TO THE LEFT. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 070/20. HELENE SHOULD CONTINUE GENERALLY EAST-NORTHEASTWARD TO NORTHEASTWARD FOR 72 HR IN DEEP SOUTHWESTERLY FLOW. AFTER THAT TIME...THERE IS SERIOUS DIVERGENCE IN THE MODEL FORECASTS. THE 12Z ECMWF...THE 18Z GFS...AND THE 18Z NOGAPS ALL TURN HELENE SOUTHWARD AND PASS NEAR OR OVER THE AZORES. ON THE OTHER HAND...THE 12Z UKMET...THE 18Z GFDL...AND THE 18Z GFS ENSEMBLE-MEAN ALL FORECAST HELENE TO CONTINUE NORTHEASTWARD. SINCE THE 18Z GFS AND NOGAPS RUNS SHOW MAJOR CHANGES FROM THEIR PREVIOUS RUNS THAT TOOK HELENE NORTHEASTWARD...IT IS TOO SOON TO MAKE MAJOR CHANGES TO THE FORECAST TRACK. THUS...THE NEW TRACK CALLS FOR A CONTINUED NORTHEASTWARD MOTION AFTER 72 HR. THE NEW TRACK IS SOUTH OF THE PREVIOUS TRACK AND IN BEST AGREEMENT WITH THE UKMET. SATELLITE IMAGERY SHOWS COLD AIR STRATOCUMULUS CLOUDS WEST OF THE CENTER...SUGGESTING THE THE COLD FRONT THAT THE LARGE-SCALE MODELS HAVE BEEN FORECASTING TO INTERACT WITH THE STORM MAY BE A LITTLE STRONGER THAN PREVIOUSLY EXPECTED. THIS HAS LED TO AN EARLIER EXTRATROPICAL TRANSITION THAN FORECAST 24-48 HR AGO. ALTHOUGH THE LARGE-SCALE MODEL GUIDANCE SUGGESTS THAT HELENE MAY KEEP A WARM CORE OF SOME TYPE FOR THE NEXT 3-4 DAYS...IT IS EXPECTED THAT ENOUGH COLD AIR WILL ENTRAIN INTO THE STORM TO COMPLETE EXTRATROPICAL TRANSITION IN 12-24 HR. HELENE WILL LIKELY STRENGTHEN SOME AS AN EXTRATROPICAL LOW THROUGH 36 HR...THEN GRADUALLY WEAKEN THEREAFTER. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0300Z 36.0N 50.6W 60 KT 12HR VT 23/1200Z 37.0N 47.1W 60 KT...BECOMING EXTRATROPICAL 24HR VT 24/0000Z 38.5N 42.6W 65 KT...EXTRATROPICAL 36HR VT 24/1200Z 40.0N 38.0W 65 KT...EXTRATROPICAL 48HR VT 25/0000Z 42.1N 33.7W 60 KT...EXTRATROPICAL 72HR VT 26/0000Z 45.5N 26.0W 55 KT...EXTRATROPICAL 96HR VT 27/0000Z 49.0N 18.0W 45 KT...EXTRATROPICAL 120HR VT 28/0000Z 53.0N 12.0W 40 KT...EXTRATROPICAL $$ FORECASTER BEVEN |
