Hurricane HELENE

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE HELENE DISCUSSION NUMBER  28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
500 AM EDT TUE SEP 19 2006
 
AS NOTED IN THE PREVIOUS DISCUSSION...THE CLOUD PATTERN ASSOCIATED
WITH HELENE HAS BECOME ELONGATED NORTH TO SOUTH.  A 0449 UTC
AQUA MICROWAVE OVERPASS SUGGESTED THAT THE EYEWALL WAS OPEN TO THE
SOUTHWEST...BUT THERE HAS BEEN LITTLE OVERALL CHANGE IN THE
SATELLITE APPEARANCE AROUND THE CORE OF THE HURRICANE.  DVORAK
INTENSITY T-NUMBERS REMAIN 5.5 FROM ALL AGENCIES AND THE INITIAL
INTENSITY WILL REMAIN 100 KT.  CONDITIONS APPEAR FAVORABLE FOR
FURTHER STRENGTHENING AS SHEAR IS FORECAST TO REMAIN LIGHT AND SSTS
WARM.  THE OFFICIAL INTENSITY FORECAST IS A LITTLE HIGHER THAN THE
AVAILABLE GUIDANCE AND IT IS POSSIBLE THAT HELENE COULD BECOME A
CATEGORY 4 HURRICANE DURING THE NEXT DAY OR TWO.
 
THE ANTICIPATED WESTWARD MOTION APPEARS TO HAVE STARTED AS INDICATED
BY AN INITIAL MOTION OF 285/7.  IN FACT...THE MOTION OVER THE PAST
FEW HOURS HAS BEEN NEARLY DUE WEST.  THE DYNAMICAL MODELS AGREE ON
A GENERAL WESTWARD MOVEMENT DURING THE NEXT 24 HOURS AS A
MID-TROPOSPHERIC RIDGE TEMPORARILY BUILDS NORTH OF HELENE AS
HURRICANE GORDON CONTINUES TO MOVE EASTWARD.  THE GFDL MODEL
ACTUALLY FORECASTS A SLIGHTLY SOUTH OF DUE WEST MOTION TODAY.  IN A
COUPLE OF DAYS...THE RIDGE IS FORECAST TO SHIFT EASTWARD AS A LARGE
MID- TO UPPER-LEVEL TROUGH APPROACHES THE EAST COAST OF THE UNITED
STATES.  THIS SHOULD ALLOW THE HURRICANE TO TURN NORTHWARD AND
EVENTUALLY NORTHEASTWARD AHEAD OF THIS TROUGH.  THE OFFICIAL
FORECAST IS VERY CLOSE TO THE PREVIOUS ADVISORY THROUGH 36
HOURS...THEREAFTER IT IS ADJUSTED A LITTLE EASTWARD CLOSE TO THE
MODEL CONSENSUS AND THE GFDL TRACK.  AT DAYS 4 AND 5...THE NHC
FORECAST IS A LITTLE FASTER THAN THE PREVIOUS ADVISORY AND IS CLOSE
TO THE GFS ENSEMBLE MEAN...BUT IT IS NOT AS FAST AS THE OPERATIONAL
GFS OR GFDL MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/0900Z 24.4N  52.1W   100 KT
 12HR VT     19/1800Z 24.6N  53.4W   105 KT
 24HR VT     20/0600Z 25.1N  55.0W   110 KT
 36HR VT     20/1800Z 26.4N  56.3W   110 KT
 48HR VT     21/0600Z 28.3N  57.1W   110 KT
 72HR VT     22/0600Z 33.6N  56.1W   100 KT
 96HR VT     23/0600Z 38.0N  52.0W    90 KT
120HR VT     24/0600Z 42.0N  45.0W    80 KT
 
$$
FORECASTER BROWN/STEWART
 
NNNN