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| #112771 (Received by flhurricane at: 10:28 AM 24.Sep.2006) TCDAT3 TROPICAL STORM HELENE DISCUSSION NUMBER 50 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 AM EDT SUN SEP 24 2006 CONVECTION CONTINUES TO SLOWLY WEAKEN NEAR THE CENTER OF HELENE. LATEST SATELLITE IMAGERY INDICATES THAT THE SYSTEM HAS ACQUIRED DEFINITIVE FRONTAL FEATURES WITH EXTENSIVE COLD AIR ADVECTION OVER THE SOUTHWESTERN SEMICIRCLE...AS EVIDENCED BY THE LARGE STRATOCUMULUS FIELD. MOREOVER...A QUIKSCAT PASS FROM AROUND 0900 UTC SUGGESTED THE STRONGEST WINDS WERE BECOMING REMOVED FROM THE CENTER...AND THE WIND FIELD IS EXPANDING AS IS TYPICAL OF AN EXTRATROPICAL CYCLONE. ALTHOUGH MICROWAVE DATA AND MODEL ANALYSES BASED ON THESE DATA IS SHOWING A WARM CORE...WE BELIEVE THIS IS DUE TO A WARM SECLUSION THAT IS COMMON IN STRONG EXTRATROPICAL CYCLONES. BASED ON THE ABOVE ANALYSES...THE EXTRATROPICAL TRANSITION IS CONSIDERED COMPLETE... AND THIS WILL BE THE LAST ADVISORY ISSUED BY THE NATIONAL HURRICANE CENTER ON HELENE. THE INITIAL MOTION IS 055/18...A LITTLE SLOWER THAN BEFORE. DYNAMICAL MODELS SHOW ADDITIONAL SLOWING OF THE FORWARD SPEED AS THE SYSTEM INTERACTS WITH AN UPSTREAM SHORTWAVE TROUGH. GUIDANCE REMAINS IN FAIRLY GOOD AGREEMENT THROUGH 48 HOURS AND THEN BEGINS TO DIVERGE AT THE EXTENDED RANGES. IN LIGHT OF THE MODEL SPREAD...THE OFFICIAL FORECAST IS CLOSE TO THE MODEL CONSENSUS. THE AFOREMENTIONED QUIKSCAT PASS SHOWED ONLY A COUPLE 65 KT VECTORS AND...ASSUMING GRADUAL WEAKENING SINCE THE TIME OF THOSE OBSERVATIONS...THE INITIAL INTENSITY IS LOWERED TO 60 KT. A CONTINUED SOURCE OF BAROCLINIC ENERGY SHOULD MAINTAIN THE CYCLONE WITH ONLY SLOW WEAKENING OVER THE NEXT DAY OR SO UNTIL IT COMBINES WITH ANOTHER EXTRATROPICAL CYCLONE OVER THE EASTERN NORTH ATLANTIC. ADDITIONAL INFORMATION ON THIS SYSTEM CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE OCEAN PREDICTION CENTER UNDER AWIPS/WMO HEADERS NFDHSFAT1/FZNT01 KWBC AND BY METEOFRANCE UNDER WMO HEADER FQNT50 LFPW. FORECAST POSITIONS AND MAX WINDS INITIAL 24/1500Z 40.9N 37.5W 60 KT...EXTRATROPICAL 12HR VT 25/0000Z 42.5N 34.6W 60 KT...EXTRATROPICAL 24HR VT 25/1200Z 43.6N 31.8W 55 KT...EXTRATROPICAL 36HR VT 26/0000Z 44.2N 28.0W 50 KT...EXTRATROPICAL 48HR VT 26/1200Z 45.1N 23.7W 45 KT...EXTRATROPICAL 72HR VT 27/1200Z 48.5N 14.0W 40 KT...EXTRATROPICAL 96HR VT 28/1200Z...MERGED WITH EXTRATROPICAL SYSTEM $$ FORECASTER RHOME/PASCH |
