410 
 WTNT43 KNHC 012058
 TCDAT3
 TROPICAL STORM FIONA DISCUSSION NUMBER   9
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082010
 500 PM AST WED SEP 01 2010
  
 THOUGH THE SATELLITE APPEARANCE OF FIONA LOOKS QUITE DISHEVELED WITH
 THE SURFACE CIRCULATION POPPING OUT FROM UNDER THE DEEP
 CONVECTION...THE AIR FORCE HURRICANE HUNTER AIRCRAFT OBSERVATIONS
 SHOW THAT THE SYSTEM STILL IS MAINTAINING MODERATE TROPICAL STORM
 INTENSITY. PEAK 850 MB FLIGHT LEVEL WINDS OF 57 KT AND SFMR SURFACE
 WIND ESTIMATES OF ABOUT 50 KT INDICATE THAT FIONA REMAINS AT 50 KT.
 AIRCRAFT OBSERVATIONS ALSO INDICATE THAT FIONA IS RATHER SMALL IN
 HORIZONTAL EXTENT WITH TROPICAL STORM FORCE WINDS EXTENDING OUT
 LESS THAN 100 NM ON AVERAGE AROUND THE SYSTEM.
 
 CURRENT MOTION OF THE CYCLONE IS A SPEEDY 17 KT TOWARD THE
 NORTHWEST.  THE SYSTEM IS BEING ADVECTED ALONG MAINLY BY THE RIDGE
 TO ITS NORTHEAST WITH SOME CONTRIBUTION OF STEERING AS WELL BY THE
 MUCH LARGER HURRICANE EARL.  THE MODEL GUIDANCE IS IN GOOD
 AGREEMENT THROUGH TWO DAYS THAT THE CYCLONE WILL CONTINUE TOWARD
 THE NORTHWEST AT A SLOWER FORWARD SPEED.  AFTER THAT...THE
 SOLUTIONS DIVERGE WITH SOME GUIDANCE QUICKLY HAVING FIONA ABSORBED
 WITHIN THE CIRCULATION OF EARL AND SOME KEEPING FIONA AS A DISTINCT
 VORTEX AND EVENTUALLY BECOMING A FRONTAL LOW IN ABOUT FOUR TO FIVE
 DAYS.  THE FORECAST TRACK IS CLOSE TO THE MODEL CONSENSUS...MINUS
 THE GFDN HURRICANE MODEL WHICH TAKES FIONA UNREALISTICALLY DUE
 WEST...AND IS SIMILAR TO THE PREVIOUS ADVISORY.
 
 THE INTENSITY FORECAST IS...AS USUAL...A DIFFICULT CALL. DESPITE THE
 CYCLONE REMAINING OVER QUITE WARM WATERS FOR THE NEXT SEVERAL
 DAYS...THE VERTICAL SHEAR APPEARS TO BE THE LIMITING FACTOR FOR THE
 INTENSITY OF FIONA. A RESEARCH MISSION BY THE NSF GULFSTREAM-V JET
 SHOWED UNIDIRECTIONAL 35 KT EASTERLIES ADVECTING OVER THE TOP OF
 THE CYCLONE. SUCH UPPER LEVEL FLOW...ALONG WITH THE FAST FORWARD
 SPEED...SHOULD LIMIT ANY INTENSIFICATION IN THE NEAR TERM AND THE
 FORECAST INTENSITY SHOWS LITTLE CHANGE FOR THE NEXT TWO DAYS. AFTER
 THAT...IT IS ANTICIPATED THAT FIONA WILL GRADUALLY DECAY AS IT GETS
 ENTRAINED INTO THE CIRCULATION OF EARL AND VERTICAL WIND SHEAR
 INCREASES. THE INTENSITY FORECAST IS SIGNIFICANTLY BELOW THE MODEL
 CONSENSUS BUT IS QUITE SIMILAR TO THE PREVIOUS ADVISORY. IF CURRENT
 TRENDS CONTINUE...IT IS EVEN POSSIBLE THAT FIONA WILL NO LONGER
 HAVE A CLOSED SURFACE CIRCULATION. UNDER THIS SCENARIO...
 ADVISORIES...AND FIONA...WOULD CEASE TO EXIST.
   
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      01/2100Z 20.2N  62.9W    50 KT
  12HR VT     02/0600Z 21.6N  64.6W    50 KT
  24HR VT     02/1800Z 23.8N  66.3W    50 KT
  36HR VT     03/0600Z 25.9N  67.4W    50 KT
  48HR VT     03/1800Z 27.4N  67.6W    45 KT
  72HR VT     04/1800Z 30.0N  66.5W    35 KT
  96HR VT     05/1800Z 33.5N  64.5W    25 KT
 120HR VT     06/1800Z...DISSIPATED
  
 $$
 FORECASTER LANDSEA/BLAKE