000
WTNT43 KNHC 311439
TCDAT3
TROPICAL STORM FIONA DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082010
1100 AM AST TUE AUG 31 2010
 
A 0929 UTC SSMIS MICROWAVE OVERPASS SHOWED CURVED BANDS OF
CONVECTION LOOSELY WRAPPING AROUND THE CENTER. SINCE THAT TIME
VISIBLE SATELLITE IMAGERY INDICATES THAT THE CONVECTIVE BANDS NEAR
THE CENTER HAVE WEAKENED...WHILE NEW CONVECTION HAS DEVELOPED
AROUND THE PERIPHERY OF THE CIRCULATION.  THE INITIAL INTENSITY
REMAINS 35 KT...BASED ON THE EARLIER SCATTEROMETER DATA.  AN AIR
FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO 
INVESTIGATE FIONA THIS AFTERNOON AND SHOULD PROVIDE A BETTER
ASSESSMENT OF THE CURRENT STRUCTURE AND INTENSITY.

THE INITIAL MOTION ESTIMATE IS 285/21 KT.  THE CYCLONE IS FORECAST
TO SLOW DOWN AND TURN NORTHWESTWARD DURING THE NEXT 24 HOURS AS IT
NEARS THE WESTERN PORTION OF THE SUBTROPICAL RIDGE.  THEREAFTER...
FIONA IS EXPECTED TO TURN NORTH-NORTHWESTWARD...THEN NORTHWARD
BETWEEN THE WESTERN SIDE OF THE RIDGE AND HURRICANE EARL TO THE
NORTHWEST.  THE TRACK GUIDANCE IS IN BETTER AGREEMENT ON THIS
SCENARIO AND THE OFFICIAL FORECAST HAS BEEN ADJUSTED EASTWARD ALONG
THE LEFT SIDE OF THE GUIDANCE ENVELOPE.  LATE IN THE FORECAST
PERIOD...FIONA SHOULD TURN NORTHEASTWARD AS DEEP SOUTHWESTERLY FLOW
DEVELOPS OVER THE WESTERN ATLANTIC.

THERE APPEARS TO BE A SMALL WINDOW OF OPPORTUNITY FOR FIONA TO
STRENGTHEN DURING THE NEXT 12 TO 24 HOURS BEFORE AN UPPER-LEVEL
RIDGE TO THE NORTHWEST OF FIONA STRENGTHENS...AND NORTHEASTERLY
UPPER-LEVEL WINDS INCREASE.  THE SHEAR IS FORECAST TO REMAIN
MODERATE TO STRONG THROUGHOUT MOST OF THE FORECAST PERIOD AND NO
ADDITIONAL STRENGTHENING IS PREDICTED.  AN ALTERNATE SCENARIO...AS
SHOWN BY THE GFS...IS THAT FIONA COULD WEAKEN AND POSSIBLY
DISSIPATE IN A COUPLE OF DAYS DUE TO THE AFOREMENTIONED SHEAR.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      31/1500Z 15.9N  55.3W    35 KT
 12HR VT     01/0000Z 16.9N  58.2W    40 KT
 24HR VT     01/1200Z 18.7N  61.3W    45 KT
 36HR VT     02/0000Z 21.1N  63.8W    45 KT
 48HR VT     02/1200Z 23.4N  65.8W    45 KT
 72HR VT     03/1200Z 27.7N  67.8W    45 KT
 96HR VT     04/1200Z 31.0N  67.5W    45 KT
120HR VT     05/1200Z 34.0N  66.0W    45 KT
 
$$
FORECASTER BROWN