687 
 WTNT43 KNHC 231445
 TCDAT3
 HURRICANE HELENE DISCUSSION NUMBER  46
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
 1100 AM EDT SAT SEP 23 2006
 
 HELENE APPEARS WELL ON ITS WAY TO BECOMING AN EXTRATROPICAL CYCLONE.
 HOWEVER...SATELLITE IMAGERY SHOWS THAT A SMALL AREA OF DEEP
 CONVECTION CONTINUES OVER AND JUST NORTH OF THE CENTER. SINCE THE
 STRUCTURE APPEARS UNCHANGED SINCE THE 0915 UTC QUIKSCAT PASS THAT
 SHOWED 80 KT MAXIMUM WINDS...THE INITIAL INTENSITY IS HELD AT 80
 KT. UNTIL THE INNER CORE CONVECTION DISSIPATES...WHICH COULD HAPPEN
 AT ANY TIME...HELENE WILL BE CLASSIFIED AS A TROPICAL CYCLONE. ONCE
 EXTRATROPICAL TRANSITION IS COMPLETE...WHICH WE ANTICIPATE WILL
 HAPPEN LATER TODAY...GRADUAL WEAKENING IS EXPECTED AS THE WIND
 FIELD SPREADS OUT. HOWEVER...THE OFFICIAL FORECAST STILL CALLS FOR
 EXTRATROPICAL HELENE TO PRODUCE SUSTAINED WINDS OF HURRICANE FORCE
 FOR THE NEXT COUPLE OF DAYS. EVEN THOUGH THE CENTER OF THE CYCLONE
 IS EXPECTED TO PASS NORTH OF THE AZORES DURING THE NEXT 2
 DAYS...THE LARGE AND EXPANDING WIND FIELD MEANS THAT GALE FORCE
 WINDS COULD AFFECT THE AZORES BEGINNING ON SUNDAY.  BEYOND 48
 HOURS...WEAKENING COULD BECOME MORE RAPID AS GLOBAL MODELS SUGGEST
 THE CYCLONE WILL LOSE ITS BAROCLINIC SUPPORT. 
 
 HELENE IS MOVING RIGHT ALONG THE PREVIOUS FORECAST TRACK WITH AN
 INITIAL MOTION ESTIMATE OF 065/20.  THERE HAS BEEN LITTLE CHANGE IN
 THE TRACK FORECAST PHILOSOPHY IN THE SHORT-TERM...AND GUIDANCE
 REMAINS TIGHTLY CLUSTERED THROUGH 48 HOURS.  THEREAFTER...THE TRACK
 GUIDANCE BEGINS TO DIVERGE WITH CONSIDERABLE SPREAD BY DAY 5.  THE
 NOGAPS MODEL FORECASTS HELENE TO MERGE WITH ANOTHER EXTRATROPICAL
 SYSTEM RESULTING IN A NORTHWARD TURN.  CONVERSELY...THE UKMET AND
 ECMWF MODELS FORECAST A LARGE UPPER-LEVEL CLOSED LOW TO DEVELOP
 EAST OF THE AZORES RESULTING IN EXTRATROPICAL HELENE TURNING SOUTH.
 AT THIS TIME...IT IS DIFFICULT TO DETERMINE IF EITHER OF THESE
 OUTLIER SCENARIOS IS MORE PLAUSIBLE.  ACCORDINGLY...THE OFFICIAL
 FORECAST LIES IN BETWEEN THESE TWO EXTREMES AND IS NEAR BOTH THE
 DYNAMICAL MODEL CONSENSUS AND THE GFS ENSEMBLE MEAN. COMPARED TO
 THE PREVIOUS ADVISORY...THIS REPRESENTS A SOUTHWARD ADJUSTMENT AND
 A SLOWER FORWARD MOTION AT THE END OF THE FORECAST. GIVEN THE LARGE
 SPREAD OF THE DYNAMICAL MODELS...THERE IS CONSIDERABLE UNCERTAINTY
 IN THE OFFICIAL TRACK FORECAST.    
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      23/1500Z 37.7N  46.4W    80 KT
  12HR VT     24/0000Z 38.9N  43.0W    80 KT...EXTRATROPICAL
  24HR VT     24/1200Z 40.7N  38.5W    75 KT...EXTRATROPICAL
  36HR VT     25/0000Z 42.5N  34.2W    70 KT...EXTRATROPICAL
  48HR VT     25/1200Z 44.1N  30.7W    65 KT...EXTRATROPICAL
  72HR VT     26/1200Z 47.0N  23.0W    55 KT...EXTRATROPICAL
  96HR VT     27/1200Z 49.0N  18.0W    45 KT...EXTRATROPICAL
 120HR VT     28/1200Z 50.5N  13.0W    40 KT...EXTRATROPICAL
  
 $$
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