Tropical Storm HELENE

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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
 
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FORECASTER RHOME/PASCH
 
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