064 
 WTNT43 KNHC 150250
 TCDAT3
 TROPICAL STORM HELENE DISCUSSION NUMBER  11
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
 1100 PM EDT THU SEP 14 2006
  
 THE INITIAL MOTION REMAINS 285/13...BASED PRIMARILY ON MICROWAVE
 SATELLITE FIX POSITIONS. THE 18Z NHC MODEL GUIDANCE HAS LESS SPREAD
 NOW THAN PREVIOUS ADVISORIES...WITH THE GFS AND NOGAPS MODELS
 HAVING SHIFTED MORE WESTWARD AND CLOSER TO THE UKMET 12Z SOLUTION.
 THE NEW 18Z UKMET RUN IS ALSO MUCH SLOWER NOW AND VERY SIMILAR TO
 THE 18Z NOGAPS MODEL RUN. THE KEY PLAYER DURING THE FORECAST CYCLE
 IS THE MID-LEVEL SHORTWAVE TROUGH CURRENTLY OVER THE NORTHEASTERN
 U.S. THAT IS FORECAST BY ALL OF THE MODELS TO DIG SOUTHEASTWARD AND
 CUTOFF INTO A LOW PRESSURE SYSTEM. HOWEVER...THE UKMET AND NOGAPS
 MODELS ARE NOW WEAKENING THE LOW AND LIFTING IT OUT SOONER THAN THE
 GFS...ECMWF... GFDL...AND CANADIAN MODELS. GIVEN THAT THE
 MID-LATITUDE FLOW ACROSS THE NORTHERN U.S. AND THE NORTH ATLANTIC
 IS FORECAST BY ALL THE MODELS TO BE FAST ZONAL FLOW...LESS
 AMPLIFICATION OF THE TROUGH SEEMS MORE REASONABLE...WHICH SHOULD
 DECREASE THE EFFECT OF ANY NORTHWARD STEERING FLOW ON THE WAST SIDE
 OF THE TROUGH. THE RESULT IS THAT THE STEERING FLOW SHOULD WEAKEN
 CONSIDERABLY BY 96 AND 120 HOURS AS MID-LEVEL RIDGING BUILDS SLOWLY
 WESTWARD TO THE NORTH OF HELENE. THE OFFICIAL FORECAST TRACK IS A
 LITTLE SOUTH OF THE PREVIOUS TRACK AND IS CLOSE TO THE GUNA AND
 CONU MODEL CONSENSUS FORECAST TRACKS.
 
 HELENE HAS BEEN HAVING A DIFFICULT TIME MAINTAINING CENTRAL DEEP
 CONVECTION FOR MORE THAN A JUST FEW HOURS AT A TIME DUE TO A LARGE
 SLUG OF DRY AIR PUNCHING INTO THE SOUTHERN AND EASTERN QUADRANTS OF
 THE CYCLONE. SINCE THIS PATTERN SEEMS TO BE UNLIKELY TO CHANGE ANY
 TIME SOON...THE INTENSITY FORECAST WAS DECREASED SLIGHTLY DURING
 THE FIRST 72 HOURS SIMILAR TO THE SHIPS MODEL. AFTER THAT... A
 SLIGHTLY FASTER RATE OF INTENSIFICATION IS FORECAST AS PER THE GFDL
 AND FSU MODELS...WHICH SEEMS REASONABLE SINCE HELENE WILL BE MOVING
 OVER 28C AND WARMER SSTS AND ALSO BE UNDERNEATH A VERY FAVORABLE
 UPPER-LEVEL OUTFLOW REGIME.
 
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      15/0300Z 14.5N  38.9W    40 KT
  12HR VT     15/1200Z 15.3N  40.8W    45 KT
  24HR VT     16/0000Z 16.4N  43.2W    50 KT
  36HR VT     16/1200Z 17.5N  45.2W    60 KT
  48HR VT     17/0000Z 18.5N  46.7W    70 KT
  72HR VT     18/0000Z 20.3N  49.4W    80 KT
  96HR VT     19/0000Z 22.4N  51.9W    90 KT
 120HR VT     20/0000Z 24.5N  54.0W    90 KT
  
 $$
 FORECASTER STEWART