Hurricane HELENE

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HURRICANE HELENE DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
1100 AM EDT SUN SEP 17 2006
 
VISIBLE SATELLITE IMAGES SHOW THAT HELENE HAS DEVELOPED A LARGE
RAGGED EYE SURROUNDED BY A RING OF DEEP CONVECTION. SATELLITE
INTENSITY ESTIMATES FROM ALL AGENCIES HAVE INCREASED TO 5.0 ON THE
DVORAK SCALE. THE 3-HOUR AVERAGE ADVANCED OBJECTIVE TECHNIQUE FROM
THE UNIVERSITY OF WISCONSIN IS 5.6. ON THIS BASIS...THE INITIAL
INTENSITY HAS BEEN INCREASED TO 90 KNOTS. THERE IS A CHANCE FOR AN 
ADDITIONAL STRENGTHENING DURING THE NEXT DAY OR TWO BEFORE THE
SHEAR INCREASES AS SUGGESTED BY SHIPS MODEL. THE OCEAN IS EXPECTED
TO REMAIN WARM ALONG THE FORECAST TRACK.

HELENE IS MOVING TOWARD THE NORTHWEST OR 305 DEGREES AT 9 KNOTS. THE
FORECAST SCENARIO COULD BE DESCRIBED AS SUCH...HELENE CURRENTLY
LOCATED ON THE SOUTHWESTERN EDGE A SUBTROPICAL RIDGE AND MOVING
TOWARD A WEAKNESS CAUSED BY A SHARP MID-LEVEL SHORT WAVE JUST EAST
OF THE UNITED STATES CAST. THEN...AS THE SHORT WAVE MOVES OUT THE
AREA...THE RIDGE WILL LIKELY BUILD WESTWARD FORCING HELENE TO
TEMPORARILY TURN MORE TO THE WEST-NORTHWEST. AFTER 3 DAYS...A
LARGER TROUGH IS EXPECTED TO MOVE EASTWARD AND FINALLY PICK UP
HELENE. THE DILEMMA IS HOW FAR WEST WILL HELENE GO SINCE TWO GOOD
MODELS DIVERGE...PUTTING ME BETWEEN A ROCK AND HARD PLACE. THE GOOD
GFS AND THE GFS ENSEMBLE MEAN HAVE THE WESTERNMOST SOLUTIONS WHILE
THE OUTSTANDING AND HARD TO BEAT GFDL HAS HELENE TURNING NORTHWARD
FARTHER EAST. SINCE THE REST OF THE GUIDANCE IS IN BETWEEN THESE
TWO EXTREME OPTIONS...THE OFFICIAL FORECAST DOES IT AS WELL.  
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/1500Z 20.5N  49.0W    90 KT
 12HR VT     18/0000Z 21.3N  50.1W    95 KT
 24HR VT     18/1200Z 22.5N  51.5W   100 KT
 36HR VT     19/0000Z 23.0N  53.0W   100 KT
 48HR VT     19/1200Z 23.5N  54.5W    95 KT
 72HR VT     20/1200Z 24.5N  57.0W    90 KT
 96HR VT     21/1200Z 27.0N  59.0W    85 KT
120HR VT     22/1200Z 30.0N  59.5W    80 KT
 
$$
FORECASTER AVILA
 
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