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TROPICAL STORM HELENE DISCUSSION NUMBER  13
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT THU SEP 21 2000
 
AN AIR FORCE RESERVE HURRICANE HUNTER FOUND 58 KT WINDS AT 1500 FT
NORTHEAST OF THE CENTER...WHICH CONFIRMED EARLIER BUOY REPORTS THAT
THE CYCLONE WAS STRENGTHENING.  THE CENTRAL PRESSURE WAS 1007 MB. 
HOWEVER...THE PLANE OBSERVED 1006 MB AT A COUPLE OF OTHER LOCATIONS.
TROPICAL DEPRESSION TWELVE IS UPGRADED TO TROPICAL STORM HELENE WITH
45 KT WINDS.

THE INITIAL MOTION IS 340/11.  THE LARGE DEEP LAYER ANTICYCLONE EAST
OF HELENE SHOULD CONTINUE IT ON A GENERAL NORTHERLY TRACK FOR 24
HR...FOLLOWED BY A TURN TO THE NORTHEAST.  WATER VAPOR IMAGERY SHOWS
THE SHORTWAVE TROUGH OVER THE EASTERN U.S. BY-PASSING THE STORM...SO
THERE LIKELY WILL BE NO SIGNIFICANT ACCELERATION DURING THE FORECAST
PERIOD.  MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THIS SCENARIO UP
TO LANDFALL...WITH SOME DIVERGENCE AFTER LANDFALL OVER HOW SHARPLY
EASTWARD HELENE WILL TURN.  THE OFFICIAL FORECAST GOES WITH A MORE
EASTWARD GROUP OF MODEL TRACKS AFTER LANDFALL...AND IS NUDGED A
LITTLE EAST OF THE PREVIOUS PACKAGE.  THE FORECAST TRACK WOULD BRING
THE CENTER TO THE WESTERN FLORIDA PANHANDLE COAST IN ABOUT 24 HR. 
THUS...WARNINGS ARE BEING ISSUED FROM THE MOUTH OF THE PEARL RIVER
TO THE MOUTH OF THE AUCILLA RIVER.
 
DESPITE THE STRENGTHENING...THE LOW LEVEL CENTER IS STILL NEAR THE
NORTHWEST EDGE OF THE CONVECTION.  SATELLITE IMAGERY AND MODEL
OUTPUT SHOW MODERATE UPPER LEVEL WESTERLIES OVER THE GULF BETWEEN
HELENE AND THE COAST...WITH STRONGER WESTERLIES OVER THE COASTAL
REGION.  THIS MAKES IT UNLIKELY...BUT NOT IMPOSSIBLE...THAT HELENE
WILL BECOME A HURRICANE BEFORE LANDFALL.  THE INTENSITY FORECAST
TAKES HELENE UP TO 55 KT AT LANDFALL IN GOOD AGREEMENT WITH THE
SHIPS MODEL.

THE HURRICANE HUNTER HAS NOT YET COMPLETED A FULL FLIGHT PATTERN...
SO THE WIND RADII MAY HAVE TO BE REVISED ON THE NEXT ADVISORY.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     21/1500Z 26.6N  87.2W    45 KTS
12HR VT     22/0000Z 28.3N  87.5W    50 KTS
24HR VT     22/1200Z 30.4N  87.0W    55 KTS
36HR VT     23/0000Z 32.0N  85.5W    30 KTS...INLAND
48HR VT     23/1200Z 33.5N  82.5W    20 KTS...DISSIPATING
72HR VT     24/1200Z...DISSIPATED 
 
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