Tropical Storm HELENE

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TROPICAL STORM HELENE DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
1100 PM EDT FRI SEP 15 2006
 
THE INITIAL MOTION ESTIMATE IS 300/12. HELENE APPEARS TO BE ON TRACK
BASED ON A PLETHORA OF MICROWAVE SATELLITE DATA. THE INITIAL
POSITION...HOWEVER...IS SOUTH OF THE CONVENTIONAL SATELLITE FIXES
WHICH APPEAR TO BE A REFLECTION OF A MID-LEVEL CIRCULATION CENTER.
MICROWAVE DATA SUGGESTS THAT THE ADVISORY MAY BE A LITTLE TOO FAR
TO THE NORTH...BUT CONTINUITY WITH THE PREVIOUS FORECAST TRACK WAS
FOLLOWED GIVEN THAT HELENE STILL HAS A BROAD LOW-LEVEL CIRCULATION
AND REDEVELOPMENT OF THE CENTER FARTHER NORTH IS STILL POSSIBLE.
OTHERWISE...THERE REMAINS LITTLE CHANGE TO THE PREVIOUS SEVERAL
FORECAST TRACKS AND REASONINGS. THE MODELS REMAIN IN EXCELLENT
AGREEMENT ON A STEADY WEST-NORTHWESTWARD MOTION FOR THE NEXT 72
HOURS. AFTER THAT...THE MODELS DIVERGE QUITE SIGNIFICANTLY WITH THE
GFDL TAKING HELENE MORE NORTHWARD...WHILE THE NOGAPS MODEL TAKES
THE CYCLONE MORE WESTWARD. THE REST OF THE MODELS ARE SPREAD OUT
EVENLY BETWEEN THOSE TWO EXTREMES. HOWEVER...ALL THE MODELS AGREE
THAT A STRONG SHORTWAVE TROUGH CURRENTLY OVER THE NORTHEASTERN U.S.
WILL MOVE SOUTHEAST AND THEN EASTWARD AND WEAKEN THE STEERING FLOW
AHEAD OF HELENE BY 96 AND 120 HOURS. THE OFFICIAL FORECAST TRACK IS
SIMILAR TO THE PREVIOUS TRACK AND THE NHC MODEL CONSENSUS.
 
THE OUTFLOW PATTERN REMAINS GOOD IN ALL QUADRANTS...WHICH USUALLY
FAVORS STEADY INTENSIFICATION. HOWEVER...DRY AIR IS STILL BEING
ENTRAINED INTO THE CENTER OF THE CYCLONE AS NOTED IN MICROWAVE
IMAGERY...SO ONLY SLOW INTENSIFICATION IS EXPECTED FOR THE NEXT 24
HOURS. AFTER THAT...DECREASING VERTICALLY SHEAR AND INCREASING SSTS
SHOULD LEAD TO MORE SIGNIFICANT INTENSIFICATION AND HELENE COULD
BECOME A MAJOR HURRICANE BY 72 HOURS...AND POSSIBLY THROUGH 120H.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      16/0300Z 17.2N  43.7W    60 KT
 12HR VT     16/1200Z 17.9N  45.1W    65 KT
 24HR VT     17/0000Z 18.9N  46.7W    70 KT
 36HR VT     17/1200Z 19.8N  48.1W    75 KT
 48HR VT     18/0000Z 20.7N  49.4W    90 KT
 72HR VT     19/0000Z 22.4N  51.8W   100 KT
 96HR VT     20/0000Z 24.0N  54.6W   100 KT
120HR VT     21/0000Z 26.0N  57.0W    95 KT
 
$$
FORECASTER STEWART
 
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