932 
 WTNT43 KNHC 150854
 TCDAT3
 TROPICAL STORM HELENE DISCUSSION NUMBER  12
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
 500 AM EDT FRI SEP 15 2006
  
 HELENE DOES NOT LOOK TOO MUCH DIFFERENT THAN IT DID SIX HOURS
 AGO...EXCEPT FOR THE DEEP CONVECTION BUBBLING IN SLIGHTLY DIFFERENT
 PORTIONS OF THE CIRCULATION.  PERHAPS SOME CONVECTION HAS RECENTLY
 INCREASED A LITTLE NEAR THE LOW-LEVEL CENTER...BUT EVEN THAT SEEMS
 TO BE ON THE DECREASE AGAIN.  THE ADVISORY INTENSITY REMAINS 40 KT
 BASED ON A BLEND OF THE 06Z DVORAK ESTIMATES.  HELENE APPEARS TO BE
 INGESTING SOME DRY AIR...AND IT MIGHT TAKE A WHILE FOR INNER CORE
 CONVECTION TO BECOME PERSISTENT.  THEREFORE...THE OFFICIAL
 INTENSITY FORECAST IS SLIGHTLY BELOW ALL OF THE AVAILABLE GUIDANCE
 AND IS ALSO A SLIGHT DOWNWARD ADJUSTMENT FROM THE PREVIOUS
 ADVISORY.  HELENE IS STILL FORECAST TO BECOME A HURRICANE IN A
 COUPLE OF DAYS...JUST NOT QUITE AS STRONG AS THE SHIPS AND GFDL ARE
 SUGGESTING.
 
 HELENE CONTINUES WEST-NORTHWESTWARD AT ABOUT 13 KT ALONG A HEADING
 BETWEEN 285 AND 290 DEGREES...WITH STEERING PROVIDED BY THE
 SUBTROPICAL RIDGE TO ITS NORTH.  THE DYNAMICAL MODELS ARE IN
 REASONABLE AGREEMENT ON A WEST-NORTHWESTWARD TO NORTHWESTWARD
 MOTION DURING THE NEXT 48 TO 72 HOURS.  AFTER THAT THE MODELS
 DIVERGE FAIRLY SIGNIFICANTLY...BOUNDED BY THE NOGAPS ON THE LEFT
 AND TURNING THE CYCLONE WESTWARD...AND THE GFDL ON THE RIGHT AND
 RACING HELENE NORTHWARD.  THE DISAGREEMENT SEEMS TO STEM FROM HOW
 EACH MODEL HANDLES A MID- TO UPPER-LEVEL TROUGH CURRENTLY OVER THE
 EASTERN UNITED STATES THAT WILL BE MOVING SLOWLY EASTWARD DURING
 THE NEXT SEVERAL DAYS.  IF THE NOGAPS IS CORRECT...ENOUGH RIDGING
 WILL REMAIN BETWEEN THAT TROUGH AND HELENE TO ALLOW THE TROPICAL
 CYCLONE TO TURN WESTWARD.  THE GFDL AND GFS...HOWEVER...FORECAST
 HELENE TO GAIN ENOUGH LATITUDE BY ROUNDING THE RIDGE SUCH THAT THE
 APPROACHING TROUGH WILL PICK UP HELENE.  I AM NOT YET CONFIDENT THE
 RIDGE TO THE NORTH OF HELENE WILL BREAK DOWN THAT FAST...SO THE NEW
 OFFICIAL TRACK FORECAST LIES ON THE LEFT SIDE OF THE MODEL GUIDANCE
 ENVELOPE...AND IT IS ESSENTIALLY IDENTICAL TO THE PREVIOUS
 ADVISORY.
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      15/0900Z 15.0N  40.3W    40 KT
  12HR VT     15/1800Z 15.9N  42.1W    45 KT
  24HR VT     16/0600Z 17.0N  44.2W    50 KT
  36HR VT     16/1800Z 18.0N  46.0W    55 KT
  48HR VT     17/0600Z 19.0N  47.4W    65 KT
  72HR VT     18/0600Z 21.0N  50.0W    75 KT
  96HR VT     19/0600Z 23.0N  52.5W    80 KT
 120HR VT     20/0600Z 24.5N  54.5W    85 KT
  
 $$
 FORECASTER KNABB