[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 211446
TCDAT3
HURRICANE HELENE DISCUSSION NUMBER  37
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
1100 AM EDT THU SEP 21 2006

THE OVERALL CLOUD PATTERN HAS CONTINUED TO DETERIORATE WITH THE
COLDEST CONVECTIVE CLOUD TOPS LOCATED PRIMARILY OVER THE EASTERN
SEMICIRCLE OF HELENE. CONSEQUENTLY...DVORAK DATA T-NUMBERS HAVE
DECREASED.  USING A BLEND OF THE DVORAK DATA T...AND CURRENT
INTENSITY NUMBERS YIELDS AN INITIAL INTENSITY ESTIMATE OF 70 KT.
AS MENTIONED IN THE PREVIOUS DISCUSSION...IT APPEARS THAT SOME
MID-LEVEL SHEAR IS AFFECTING THE HURRICANE.  DURING THE NEXT COUPLE
OF DAYS... THE SHEAR IS FORECAST TO INCREASE AND HELENE WILL BE
MOVING OVER SLIGHTLY COOLER SSTS.  ACCORDINGLY...THE SHIPS AND FSU
SUPERENSEMBLE DO NOT RESTRENGTHEN HELENE AND THE OFFICIAL FORECAST
WILL NOT EITHER.  THE NHC INTENSITY FORECAST FOLLOWS THE FSU
SUPERENSEMBLE CLOSELY THROUGH 72 HOURS...THEREAFTER IT IS A LITTLE
HIGHER THAN THE GUIDANCE AS HELENE IS EXPECTED TO BECOME A POWERFUL
EXTRATROPICAL CYCLONE.

THE INITIAL MOTION ESTIMATE IS 005/11. HELENE IS CURRENTLY ROUNDING
THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE LOCATED WELL EAST OF
THE HURRICANE.  HELENE IS FORECAST BY THE DYNAMICAL MODELS  TO
ACCELERATE NORTHEASTWARD AHEAD OF A LARGE DEEP-LAYER TROUGH THAT IS
MOVING OFF THE UNITED STATES EAST COAST.  THE GFDL REMAINS ON THE
WESTERN SIDE OF THE GUIDANCE WHILE THE UKMET AND ECMWF ARE ON THE
EASTERN SIDE.  THE OFFICIAL TRACK FORECAST IS IS VERY CLOSE TO THE
PREVIOUS ADVISORY...WHICH IS CLOSE TO THE GFS...NOGAPS...AND
FLORIDA STATE SUPERENSEMBLE.

EVEN THOUGH HELENE IS FORECAST TO RECURVE OVER THE CENTRAL ATLANTIC
OCEAN...SOME LONG PERIOD SWELLS COULD AFFECT PORTIONS OF THE EAST
COAST OF NORTH AMERICA AND BERMUDA DURING THE NEXT COUPLE OF DAYS.

FORECAST POSITIONS AND MAX WINDS

INITIAL      21/1500Z 29.6N  56.9W    70 KT
 12HR VT     22/0000Z 31.4N  56.3W    70 KT
 24HR VT     22/1200Z 34.1N  54.5W    70 KT
 36HR VT     23/0000Z 36.8N  51.2W    70 KT
 48HR VT     23/1200Z 39.6N  46.6W    65 KT...BECOMING EXTRATROPICAL
 72HR VT     24/1200Z 45.2N  36.4W    60 KT...EXTRATROPICAL
 96HR VT     25/1200Z 49.5N  28.5W    60 KT...EXTRATROPICAL
120HR VT     26/1200Z 54.0N  20.0W    55 KT...EXTRATROPICAL

$$
FORECASTER BROWN/AVILA
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