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Tropical Storm HELENE (Text)

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TROPICAL STORM HELENE DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
500 AM EDT THU SEP 14 2006
 
HELENE REMAINS A FAIRLY DISORGANIZED TROPICAL STORM.  THE
CONVECTIVE BAND SEEN LAST NIGHT IN THE NORTHWESTERN QUADRANT HAS
SPREAD OUT AND FRAGMENTED...THERE IS LITTLE OR NO DEEP
CONVECTION WITHIN ABOUT 60 N MI OF THE LOW-LEVEL CENTER...AND IN
GENERAL THE CLOUD TOPS HAVE WARMED OVERNIGHT.  DVORAK T-NUMBERS ARE
UNCHANGED AND THE ADVISORY INTENSITY REMAINS 35 KT.

THE STORM CONTINUES TO RACE WESTWARD AT 280/19 AS IT CURRENTLY LIES
SOUTH OF THE CORE OF THE SUBTROPICAL RIDGE. THE SPREAD IN THE TRACK
GUIDANCE HAS BECOME RELATIVELY LARGE WITH THE MODELS FALLING INTO
TWO MAIN CAMPS. THE GFS...ITS ENSEMBLE MEAN...AND THE GFDL FORECAST
THE RIDGE TO THE NORTH TO WEAKEN QUITE RAPIDLY AND ALLOW THE STORM
TO TURN NORTHWESTWARD IN ABOUT 12 HOURS. THE UKMET AND NOGAPS
MAINTAIN THE RIDGE LONGER AND FORECAST HELENE TO MAINTAIN A
WEST-NORTHWESTWARD MOTION FOR ABOUT 48 MORE HOURS. ALL OF THE
MODELS FORECAST A NORTHWESTWARD MOTION...AT ABOUT HALF THE CURRENT
FORWARD SPEED...OVER THE CENTRAL ATLANTIC DURING DAYS 3-5. BY THAT
TIME...HOWEVER...THE TRACK GUIDANCE ENVELOPE IS MORE THAN 300 MILES
WIDE...SO THE TRACK FORECAST AT THOSE LONG RANGES IS QUITE
UNCERTAIN. THE NEW OFFICIAL TRACK FORECAST IS MOVED TO THE LEFT OF
THE PREVIOUS ADVISORY...BUT NOT AS FAR AS THE MODEL CONSENSUS.

HELENE CONTINUES IN ITS STRUGGLE TO INTENSIFY...PROBABLY BECAUSE OF
ITS LARGE SIZE AND THE FAST FORWARD MOTION.  IT IS ASSUMED THAT THE
CONVECTION WILL SOON CONSOLIDATE NEAR THE CIRCULATION CENTER AND
ALLOW FOR MORE STEADY STRENGTHENING DURING THE NEXT DAY OR TWO. 
THE IMPACTS OF THE NEARBY SAHARAN AIR LAYER ARE UNCERTAIN BUT COULD
END UP BEING AN ADDITIONAL INHIBITING FACTOR.  LATER IN THE
FORECAST PERIOD...SINCE THE SSTS ALONG THE FORECAST TRACK WILL
REMAIN 27-28 CELSIUS AND THE GLOBAL MODELS INDICATE A WEAK SHEAR
ENVIRONMENT...ALL OF THE INTENSITY GUIDANCE ANTICIPATES HELENE TO
BECOME A HURRICANE. THE SHIPS MODEL HAS BACKED OFF A BIT AND NOW
MAKES HELENE NO STRONGER THAN ABOUT 85 KT THROUGH FIVE DAYS...WHICH
IS CLOSE TO THE LATEST GFDL SOLUTION. THE OFFICIAL FORECAST IS
ADJUSTED SLIGHTLY DOWNWARD TO BE IN AGREEMENT WITH THE GUIDANCE AT
THE LONGER RANGES...BUT IT IS BELOW SHIPS DURING THE FIRST 48 HOURS
OR SO.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/0900Z 13.7N  34.7W    35 KT
 12HR VT     14/1800Z 14.1N  37.0W    40 KT
 24HR VT     15/0600Z 15.2N  39.6W    50 KT
 36HR VT     15/1800Z 16.5N  41.6W    60 KT
 48HR VT     16/0600Z 17.8N  43.0W    70 KT
 72HR VT     17/0600Z 20.0N  45.5W    80 KT
 96HR VT     18/0600Z 22.0N  48.5W    85 KT
120HR VT     19/0600Z 24.0N  51.0W    85 KT
 
$$
FORECASTER KNABB
 
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