082 
 WTNT43 KNHC 140849
 TCDAT3
 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