HOME	PRODUCTS	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM HELENE DISCUSSION NUMBER  14
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT THU SEP 21 2000
 
AN EARLIER AIR FORCE RESERVE HURRICANE HUNTER OBSERVED A BURST OF
INTENSIFICATION WHERE THE CENTRAL PRESSURE DROPPED TO 999 MB WITH
FLIGHT LEVEL WINDS OF 70 KT.  SINCE THAT TIME...THE LOW LEVEL CENTER
HAS SEPARATED FROM THE CONVECTION DUE TO WESTERLY VERTICAL SHEAR. 
A NEW AIRCRAFT HAS JUST MEASURED A 998 MB PRESSURE.  THE INITIAL
INTENSITY IS SET TO 55 KT.

THE INITIAL MOTION IS 360/11.  THERE IS LITTLE CHANGE IN EITHER THE
TRACK FORECAST REASONING OR THE TRACK FORECAST FROM THE PREVIOUS
PACKAGE.  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 AND EAST-NORTHEAST AS HELENE MOVES INTO THE
WESTERLIES.  MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THIS SCENARIO.
THE FORECAST TRACK BRINGS THE CENTER TO THE WESTERN FLORIDA
PANHANDLE COAST IN ABOUT 18 HR.
 
THE NORMAL FORECAST FOR A SYSTEM THAT LOOKS LIKE HELENE CURRENTLY
DOES WOULD BE FOR LITTLE CHANGE IN STRENGTH...ESPECIALLY GIVEN THE
CURRENT UPPER LEVEL WESTERLIES.  HOWEVER...LARGE-SCALE MODELS ALL
SUGGEST THAT THE WESTERLIES MAY DECREASE JUST BEFORE LANDFALL...
WHICH WOULD OPEN THE WINDOW FOR ONE MORE ROUND OF INTENSIFICATION. 
BASED ON THIS...THE INTENSITY FORECAST CALLS FOR A LITTLE MORE
STRENGTHENING...AND THERE IS A SMALL CHANCE THAT HELENE COULD REACH
HURRICANE STRENGTH.  A COMBINATION OF LANDFALL AND INCREASING
VERTICAL SHEAR SHOULD WEAKEN HELENE AFTER 18 HR.  SINCE HELENE IS
STRONGER THAN PREVIOUSLY FORECAST...THE SYSTEM COULD SURVIVE UNTIL
IT MOVES BACK INTO THE ATLANTIC.  HOWEVER...THE UPPER LEVEL WINDS
CURRENTLY LOOK UNFAVORABLE FOR ANY KIND OR REGENERATION AT THAT
TIME.

THE HURRICANE HUNTER AND SURFACE OBSERVATIONS INDICATE HELENE HAS A
SMALL AND RATHER ASYMMETRIC WIND FIELD...THUS THE RATHER PECULIAR
LOOKING WIND RADII.

A HURRICANE WATCH HAS BEEN ISSUED FROM THE ALABAMA-FLORIDA BORDER
EASTWARD TO THE AUCILLA RIVER IN RESPONSE TO THE SOMEWHAT INCREASED
CHANCE THAN HELENE COULD BECOME A HURRICANE.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     21/2100Z 27.6N  87.2W    55 KTS
12HR VT     22/0600Z 29.2N  87.1W    60 KTS
24HR VT     22/1800Z 31.1N  86.0W    50 KTS...INLAND
36HR VT     23/0600Z 32.8N  84.1W    30 KTS...INLAND
48HR VT     23/1800Z 34.5N  80.5W    25 KTS...DISSIPATING
72HR VT     24/1800Z 38.0N  70.0W    25 KTS...DISSIPATING
 
 
NNNN