253 
 WTNT43 KNHC 221441
 TCDAT3
 HURRICANE HELENE DISCUSSION NUMBER  41
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
 1100 AM EDT FRI SEP 22 2006
  
 THE SATELLITE PRESENTATION OF HELENE HAS DEGRADED SLIGHTLY OVER THE
 LAST SEVERAL HOURS...WITH INNER CORE CONVECTION STARTING TO SPUTTER
 AND FAVOR THE NORTHEASTERN QUADRANT. ACCORDINGLY...DVORAK DATA T
 NUMBERS HAVE DECREASED...BUT THE INITIAL INTENSITY IS MAINTAINED AT
 75 KT FOR NOW IN ACCORDANCE WITH THE DVORAK CI NUMBERS. INCREASING
 VERTICAL SHEAR AND DECREASING SSTS APPEAR TO BE TAKING THEIR TOLL
 ON HELENE...AND THE CYCLONE SHOULD GRADUALLY WEAKEN AS IT SLOWLY
 LOSES TROPICAL CHARACTERISTICS DURING THE NEXT COUPLE OF DAYS. ON
 DAYS 2 AND 3...STRONG BAROCLINIC ENERGY IS EXPECTED TO LIMIT
 FURTHER WEAKENING...WITH HELENE FORECAST BY ALL THE GLOBAL MODELS
 TO BE A LARGE AND POWERFUL EXTRATROPICAL CYCLONE OVER THE OPEN
 WATERS OF THE CENTRAL NORTH ATLANTIC. IT SHOULD BE NOTED THAT THE
 PRECISE TIMING OF EXTRATROPICAL TRANSITION IS DIFFICULT TO DISCERN
 GIVEN SOME DIFFERENCES IN STRUCTURAL EVOLUTION AMONG THE
 MODELS...AS SHOWN BY THE FSU PHASE SPACE DIAGRAMS. TOWARD THE END
 OF THE FORECAST...GLOBAL MODELS SUGGEST THAT HELENE WILL LOSE SOME
 OF ITS BAROCLINIC SUPPORT WHICH WOULD INDUCE A WEAKENING TREND. THE
 OFFICIAL FORECAST SHOWS A LITTLE MORE WEAKENING DURING THE FIRST 24
 HOURS GIVEN THE RECENT TRENDS IN THE CONVECTIVE PATTERN. BEYOND 24
 HOURS...THE OFFICIAL INTENSITY FORECAST IS ESSENTIALLY AN UPDATE OF
 THE PREVIOUS ONE.
  
 HELENE IS STARTING TO ACCELERATE NORTHEASTWARD AS IT ROUNDS THE
 WESTERN PERIPHERY OF A MID-TROPOSPHERIC RIDGE...AND THE INITIAL
 MOTION ESTIMATE IS NOW 040/18. THE HURRICANE IS EMBEDDED WITHIN
 STRONG SOUTHWESTERLY FLOW AHEAD OF A MIDDLE TO UPPER-LEVEL TROUGH
 OVER THE WESTERN ATLANTIC. THE GUIDANCE REMAINS TIGHTLY CLUSTERED
 THROUGH 72 HOURS...AND MODELS ARE NOW IN BETTER AGREEMENT AT DAYS 4
 AND 5. THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE NOGAPS
 MODEL AND IS A LITTLE SLOWER AND TO THE SOUTH OF THE PREVIOUS
 ADVISORY.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      22/1500Z 34.4N  54.2W    75 KT
  12HR VT     23/0000Z 36.2N  51.6W    70 KT
  24HR VT     23/1200Z 37.9N  47.4W    65 KT
  36HR VT     24/0000Z 40.0N  42.8W    65 KT
  48HR VT     24/1200Z 42.4N  37.5W    65 KT...EXTRATROPICAL
  72HR VT     25/1200Z 47.5N  29.0W    65 KT...EXTRATROPICAL
  96HR VT     26/1200Z 52.5N  20.0W    55 KT...EXTRATROPICAL
 120HR VT     27/1200Z 56.5N  15.0W    50 KT...EXTRATROPICAL
  
 $$
 FORECASTER RHOME/KNABB