925 
 WTNT43 KNHC 210842
 TCDAT3
 HURRICANE HELENE DISCUSSION NUMBER  36
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
 500 AM EDT THU SEP 21 2006
  
 THE OVERALL CONVECTIVE PATTERN HAS DECREASED IN AREAL COVERAGE AND
 THE EYE HAS RECENTLY BECOME CLOUD-OBSCURED. SATELLITE INTENSITY
 ESTIMATES ARE 77 KT FROM ALL THREE AGENCIES...SO THE ADVISORY
 INTENSITY HAS BEEN DECREASED TO 80 KT. THE UPPER-LEVEL OUTFLOW
 PATTERN REMAINS EXCELLENT IN ALL QUADRANTS...BUT WATER VAPOR AND
 INFRARED SATELLITE IMAGERY INDICATE SOME MID-LEVEL SHEAR IS NOW
 UNDERCUTTING THE FAVORABLE OUTFLOW LAYER.
  
 THE INITIAL MOTION ESTIMATE IS 010/11. HELENE IS BEGINNING TO ROUND
 THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE SITUATED EAST-WEST
 ALONG 29N-30N LATITUDE. A DEEP-LAYER TROUGH MOVING OFF THE U.S.
 EAST COAST THAT EXTENDS FROM NEW ENGLAND SOUTHWARD TO THE SOUTHERN
 FLORIDA PENINSULA IS PROGRESSING EASTWARD AT 20-25 KT AND SHOULD
 GRADUALLY TURN HELENE NORTHEASTWARD DURING THE NEXT 24-36 HOURS...
 WITH MORE RAPID ACCELERATION EXPECTED AFTER THAT. THE OFFICIAL
 FORECAST TRACK HAS BEEN SHIFTED SLIGHTLY EASTWARD...BUT NOT NEARLY
 AS FAR EAST AND SOUTH AS THE UKMET AND ECMWF MODELS...WHICH BRING
 HELENE VERY CLOSE TO THE NORTHWESTERN AZORES IN 72-96 HOURS. THOSE
 TWO MODELS HAD A DISTINCT RIGHT BIAS DURING THE RECENT EVOLUTION OF
 FORMER HURRICANE GORDON...SO LESS WEIGHT WAS PLACED ON THOSE 
 SOLUTIONS AND THE OFFICIAL TRACK IS SIMILAR TO THE MODEL CONSENSUS. 
 
 AS HELENE BEGINS TO ACCELERATE NORTHEASTWARD...THE MID-LEVEL SHEAR
 COULD ABATE ENOUGH TO ALLOW FOR SOME SLIGHT INTENSIFICATION WHILE
 THE CYCLONE IS STILL OVER 27C SSTS. BY 72 HOURS...HOWEVER...HELENE
 IS EXPECTED TO COME UNDER THE INFLUENCE OF STRONG CYCLONIC MID- TO
 UPPER-LEVEL FLOW AND INCREASING BAROCLINIC EFFECTS...CAUSING THE
 CYCLONE TO TRANSITION OVER TO A POWERFUL EXTRATROPICAL LOW PRESSURE
 SYSTEM SIMILAR TO WHAT FORMER HURRICANE GORDON DID YESTERDAY.
  
 EVEN THOUGH HELENE IS FORECAST TO RECURVE OVER THE CENTRAL ATLANTIC
 OCEAN...SOME LONG PERIOD SWELLS COULD AFFECT PORTIONS OF THE EAST
 COAST OF NORTH AMERICA AND BERMUDA DURING THE NEXT COUPLE OF DAYS.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      21/0900Z 28.4N  56.8W    80 KT
  12HR VT     21/1800Z 30.1N  56.5W    85 KT
  24HR VT     22/0600Z 32.8N  55.3W    90 KT
  36HR VT     22/1800Z 35.6N  52.7W    85 KT
  48HR VT     23/0600Z 38.5N  48.7W    75 KT...BECOMING EXTRATROPICAL
  72HR VT     24/0600Z 43.9N  39.1W    65 KT...EXTRATROPICAL
  96HR VT     25/0600Z 48.0N  30.0W    60 KT...EXTRATROPICAL
 120HR VT     26/0600Z 53.0N  22.0W    55 KT...EXTRATROPICAL
  
 $$
 FORECASTER STEWART