Tropical Storm HELENE

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TROPICAL STORM HELENE DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
500 PM EDT THU SEP 14 2006
 
THE OVERALL CLOUD PATTERN ASSOCIATED WITH HELENE HAS NOT CHANGED
MUCH SINCE THIS MORNING...AND THERE ARE NO DISTINCT CONVECTIVE
BANDING FEATURES.  HOWEVER...THERE IS A SMALL BURST OF CONVECTION
THAT HAS RECENTLY DEVELOPED NEAR THE CENTER.  SATELLITE INTENSITY
ESTIMATES REMAIN UNCHANGED FROM THIS MORNING AND THE INITIAL
INTENSITY WILL REMAIN 40 KT.  A RATHER DISTINCT LOW-LEVEL
CIRCULATION BECAME APPARENT IN VISIBLE IMAGERY LATE THIS MORNING
WHICH WAS A LITTLE TO THE RIGHT OF THE PREVIOUS TRACK...AND THIS
REQUIRED A SLIGHT ADJUSTMENT BOTH TO THE WORKING TRACK AND TO THE
SHORT TERM FORECAST.

HELENE HAS SLOWED DOWN DURING THE PAST 6 HOURS...BUT USING A LONGER
TERM 12 HOUR AVERAGE YIELDS AN INITIAL MOTION ESTIMATE OF 285/14.
HELENE IS MOVING WEST-NORTHWESTWARD SOUTH OF A MID-TO UPPER-LEVEL
RIDGE.  THE GLOBAL MODELS IN GENERAL DEVELOP A BREAK IN THE RIDGE
IN A COUPLE DAYS BETWEEN 50W AND 60W...WHICH SHOULD IMPART A MORE
NORTHWESTWARD MOTION.  HOWEVER...THERE REMAINS A FAIRLY LARGE
SPREAD IN THE MODELS AS TO WHEN THIS MAY OCCUR.  THE GFS...ITS
ENSEMBLE MEAN...AND THE GFDL ARE TO THE RIGHT AND FORECAST THE
RIDGE TO WEAKEN MUCH SOONER.  THE UKMET KEEPS THE RIDGE INTACT
LONGER AND THEREFORE IS ON THE LEFT SIDE OF THE GUIDANCE.  THE
OFFICIAL TRACK IS CLOSE TO THE FSU SUPERENSEMBLE AND GUNA 
MODEL CONSENSUS.

EVEN THOUGH THE OUTFLOW IS WELL ESTABLISHED AND HELENE IS IN A VERY
LOW SHEAR ENVIRONMENT...THE LARGE CIRCULATION STILL LACKS INNER
CORE CONVECTION.  UNTIL THE INNER CORE DEVELOPS...STRENGTHENING IS
EXPECTED TO BE SLOW.  THE NHC INTENSITY FORECAST SHOWS AN INCREASE
IN WIND SPEED MUCH LIKE THE SHIPS MODEL.  LATE IN THE PERIOD GLOBAL
MODELS SUGGEST SOME INCREASING SHEAR WHICH COULD SLOW THE
INTENSIFICATION.  ACCORDINGLY...THE OFFICIAL FORECAST IS NOT AS
AGGRESSIVE AS THE FSU SUPERENSEMBLE AT DAYS 4 AND 5.
 
THE WIND RADII WERE ADJUSTED OUTWARD BASED ON A RECENT REPORT OF 
34 KT WINDS FROM A MOORED BUOY ABOUT 90 NM NORTHWEST OF HELENE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/2100Z 14.2N  37.6W    40 KT
 12HR VT     15/0600Z 14.8N  39.7W    45 KT
 24HR VT     15/1800Z 16.0N  42.1W    55 KT
 36HR VT     16/0600Z 17.3N  44.4W    65 KT
 48HR VT     16/1800Z 18.5N  46.2W    75 KT
 72HR VT     17/1800Z 20.5N  49.0W    85 KT
 96HR VT     18/1800Z 22.5N  51.0W    90 KT
120HR VT     19/1800Z 25.5N  54.0W    90 KT
 
$$
FORECASTER BROWN
 
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