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Hurricane HELENE


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
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
 
$$
FORECASTER RHOME/KNABB
 
NNNN


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Page last modified: Saturday, 23-Sep-2006 14:50:02 UTC