Tropical Storm FIONA

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TROPICAL STORM FIONA DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082010
500 PM AST THU SEP 02 2010
 
THERE HAS BEEN LITTLE CHANGE WITH FIONA DURING THE DAY. THE STORM
CONTINUES THE PATTERN OBSERVED DURING THE LAST DAY OR SO OF BURSTS
OF CONVECTION FORMING NEAR THE CENTER...THEN SHEARING AWAY. AN
ASCAT PASS FROM LATE THIS MORNING SHOWED MAXIMUM WINDS OF ABOUT 40
KT. GIVEN THE WELL-DOCUMENTED LOW BIAS OF THAT INSTRUMENT...45 KT
SEEMS LIKE A REASONABLE INITIAL WIND SPEED. THE INTENSITY FORECAST
IS DIFFICULT BECAUSE IT SEEMS LIKE FIONA HAS BEEN WITHSTANDING THE
SHEAR BETTER THAN MOST TROPICAL CYCLONES. THE LATEST INTENSITY
GUIDANCE DOES NOT WEAKEN THE STORM AS QUICKLY AS EARLIER...BUT IS
ACTUALLY PRETTY CLOSE TO THE PREVIOUS FORECAST. THUS NO CHANGES ARE
MADE TO THE LAST NHC FORECAST. AFTER 72 HOURS...ALL OF THE GLOBAL
MODELS SHOW THE TROPICAL CYCLONE SHEARING OUT AS IT MOVES
NORTHEASTWARD.
 
FIONA HAS TURNED A LITTLE MORE AND IS NOW MOVING 335/15.  THERE IS
NO CHANGE IN SYNOPTIC REASONING WITH THE CYCLONE MOVING AROUND A
SUBTROPICAL ANTICYCLONE.  THE STORM SHOULD TURN TOWARD THE NORTH...
THEN NORTHEAST AS IT STARTS TO MOVE INTO THE MID-LATITUDES. THE
MODELS ARE GENERALLY SLOWER THAN THE PREVIOUS CYCLE...BUT SINCE
THE CYCLONE CONTINUES SPEEDING ALONG...THE NHC FORECAST WILL STAY
ON THE FASTER SIDE OF THE GUIDANCE ENVELOPE...WITH LITTLE CHANGE TO
THE TRACK. THERE IS REASONABLE AGREEMENT THAT FIONA WILL BE CLOSE
TO BERMUDA IN 36-48 HOURS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/2100Z 25.6N  66.4W    45 KT
 12HR VT     03/0600Z 27.5N  66.8W    45 KT
 24HR VT     03/1800Z 29.7N  66.4W    45 KT
 36HR VT     04/0600Z 31.7N  65.4W    40 KT
 48HR VT     04/1800Z 33.7N  64.1W    35 KT
 72HR VT     05/1800Z 38.0N  61.0W    25 KT...DISSIPATING
 96HR VT     06/1800Z...DISSIPATED
 
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FORECASTER BLAKE/BROWN
 
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