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Tropical Storm FIONA (Text)

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TROPICAL STORM FIONA DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082010
500 PM EDT MON AUG 30 2010
 
EARLIER TODAY...ABOUT 30 DROPSONDES WERE RELEASED DURING A G-V
RESEARCH MISSION BEING CONDUCTED BY THE NATIONAL CENTER FOR
ATMOSPHERIC RESEARCH NEAR THE AREA OF LOW PRESSURE LOCATED ABOUT
800 MILES EAST OF THE LESSER ANTILLES.  ONE OF THE DROPSONDES
MEASURED A SURFACE WIND OF 35 KT APPROXIMATELY 120 N MI TO THE
NORTHEAST OF THE ESTIMATED CENTER.  THIS MEASUREMENT AGREES WITH AN
ASCAT PASS FROM 1208 UTC...WHICH SHOWED A SWATH OF 30-35 KT WINDS
IN THAT SAME AREA.  CONVECTION HAS BEEN A LITTLE THIN FOR MOST OF
THE DAY...BUT BANDING FEATURES HAVE RECENTLY BECOME MORE PROMINENT
MAINLY OVER THE WESTERN SEMICIRCLE.  GIVEN THE INCREASE IN
CONVECTION AND SINCE TROPICAL STORM FORCE WINDS ARE ALREADY
OCCURRING...THE SYSTEM IS BEING DIRECTLY UPGRADED TO TROPICAL STORM
FIONA.

SINCE FIONA STILL LACKS SOME ORGANIZATION AND THE WIND FIELD IS
SOMEWHAT LARGE...THE CYCLONE WILL LIKELY HAVE A DIFFICULT TIME
INTENSIFYING OVER THE NEXT DAY OR SO.  I DO NOT BELIEVE THIS
STRUCTURE IS HANDLED WELL BY THE STATISTICAL INTENSITY
GUIDANCE...WHICH INTENSIFY FIONA TO A HURRICANE IN 36 TO 48
HOURS...SO I AM INCLINED TO LEAN CLOSER TO THE DYNAMICAL GFDL AND
HWRF AT THIS POINT.  IN FACT...THE GFS DISSIPATES THE CYCLONE WITHIN
2 TO 3 DAYS.  THE OFFICIAL FORECAST THEREFORE SHOWS MINIMAL
STRENGTHENING OVER THE NEXT 1 TO 2 DAYS AND THEN LEVELS OUT THE
INTENSITY FOR DAYS 3 THROUGH 5...WHEN IT APPEARS THAT INCREASING
VERTICAL SHEAR COULD BECOME A LIMITING FACTOR. 

THE SURFACE CENTER HAS BEEN A LITTLE DIFFICULT TO LOCATE...AND THE
INITIAL MOTION IS AN UNCERTAIN 270/21.  TRACK MODEL GUIDANCE IS IN
GOOD AGREEMENT FOR THE NEXT 48 HOURS AND SHOWS FIONA TURNING TOWARD
THE NORTHWEST...GENERALLY FOLLOWING EARL AROUND THE WESTERN
PERIPHERY OF THE SUBTROPICAL RIDGE.  AFTER THAT...THE
GFDL...HWRF...AND GFS KEEP FIONA AS A WEAK SYSTEM AND SHOW IT
CONTINUING TO THE NORTH IN THE LOW-LEVEL FLOW BEHIND EARL.  THE
ECMWF...ON THE OTHER HAND...SHOWS A STRONGER FIONA AND SUGGESTS
THAT THE SUBTROPICAL RIDGE COULD BUILD BACK TO THE WEST BEFORE THE
CYCLONE CAN RECURVE.  THE OFFICIAL FORECAST IS VERY CLOSE TO THE
MODEL CONSENSUS TVCN FOR THE FIRST 48 HOURS BUT THEN LIES A LITTLE
NORTH OF THE CONSENSUS IN FAVOR OF THE TRACKS OF THE WEAKER GFDL
AND HWRF.
 
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/2100Z 14.4N  48.7W    35 KT
 12HR VT     31/0600Z 14.9N  51.9W    35 KT
 24HR VT     31/1800Z 15.8N  55.9W    40 KT
 36HR VT     01/0600Z 17.2N  59.2W    45 KT
 48HR VT     01/1800Z 19.3N  62.0W    45 KT
 72HR VT     02/1800Z 24.0N  66.0W    40 KT
 96HR VT     03/1800Z 27.5N  68.0W    40 KT
120HR VT     04/1800Z 29.0N  69.0W    40 KT
 
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FORECASTER BERG
 
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