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 906 
 WTNT43 KNHC 020853
 TCDAT3
 TROPICAL STORM FIONA DISCUSSION NUMBER  11
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082010
 500 AM AST THU SEP 02 2010
  
 AFTER LITTLE TO NO CONVECTION NEAR THE CENTER OF FIONA...A STRONG
 BURST OF DEEP CONVECTION DEVELOPED OVER THE CENTER FOR A FEW HOURS
 EARLIER THIS MORNING...WHICH HAS NOW BEEN SHEARED SLIGHTLY TO THE
 SOUTHWEST OF THE CENTER. HOWEVER...NIGHTTIME VISIBLE IMAGERY AND A
 02/0156Z ASCAT OVERPASS INDICATE FIONA HAS A SMALL BUT VERY
 WELL-DEFINED CIRCULATION. THE INITIAL INTENSITY OF 45 KT IS BASED
 ON A BELTON OF SATELLITE INTENSITY ESTIMATES OF 35 KT FROM FROM
 TAFB AND SAB...AT LEAST 40 KT FROM THE ASCAT PASS...AND UW-CIMSS
 ADT ESTIMATE OF 49 KT.
  
 THE INITIAL MOTION ESTIMATE IS 320/15 BASED ON MOSTLY ON MICROWAVE
 FIXES AND CONTINUITY WITH THE PREVIOUS ADVISORY MOTION. THE FUTURE
 TRACK OF FIONA IS HEAVILY DEPENDENT ON THE INTENSITY AND STRUCTURE
 OF THE CYCLONE. IT IS UNLIKELY THAT FIONA WILL GROW MUCH MORE IN
 HORIZONTAL SIZE DUE TO THE LARGE CIRCULATION OF POWERFUL HURRICANE
 EARL SITUATED ABOUT 750 NMI TO THE NORTHWEST. HOWEVER...ALL OF THE
 GLOBAL MODELS ARE NOW FORECASTING FIONA TO ROUND THE WESTERN
 PERIPHERY OF THE SUBTROPICAL RIDGE LOCATED EAST-WEST BETWEEN 27N
 AND 30N LATITUDE...AND IN 36-48 HOURS MOVE UNDERNEATH A REGION OF
 LOW VERTICAL SHEAR BETWEEN THE STRONG NORTHERLY OUTFLOW FROM EARL
 AND THE SOUTHWESTERLY FLOW AHEAD OF A LARGE MID-LATITUDE TROUGH
 FORECAST TO MOVE OFF THE U.S. EAST COAST IN 24 HOURS AND CAPTURE
 HURRICANE EARL. IF THIS PATTERN EVOLVES...FIONA WILL REMAIN A
 DISTINCT ENTITY AND NOT BECOME ABSORBED BY THE LARGE CIRCULATION OF
 EARL AS QUICKLY AS MOST OF THE GLOBAL MODELS ARE FORECASTING. THE
 HWRF AND GFDL MODELS KEEP FIONA A SEPARATE SYSTEM THROUGH 120 HOURS
 AND EVEN MAKE THE CYCLONE A HURRICANE IN 24-36 HOURS. THE OFFICIAL
 FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK THROUGH 24 HOURS...
 AND THEN A LITTLE TO EAST OR RIGHT OF TRACK AFTER THAT. ON THE
 FORECAST TRACK...FIONA IS EXPECTED TO PASS VERY NEAR BERMUDA IN
 ABOUT 48 HOURS...WHICH HAS PROMPTED THE ISSUANCE OF A TROPICAL
 STORM WATCH FOR THAT ISLAND BY THE BERMUDA WEATHER SERVICE.
 
 AS MENTIONED ABOVE...FIONA MAY REMAIN JUST WEST OF THE STRONGEST
 NORTHEASTERLY VERTICAL WIND SHEAR ASSOCIATED WITH THE OUTFLOW OF
 EARL FOR THE NEXT 24 HOURS. ALTHOUGH THERE MAY BE FLUCTUATIONS IN
 THE INTENSITY OF FIONA...THE SHEAR IS NOT EXPECTED TO BE STRONG
 ENOUGH TO STRIP AWAY ALL OF THE CONVECTION. BY 36-48 HOURS...FIONA
 MAY MOVE INTO THE AFOREMENTIONED REGION OF LOW SHEAR BENEATH A
 SMALL UPPER-LEVEL ANTICYCLONE FORECAST BY ALL THE MODELS TO DEVELOP
 NEAR BERMUDA. THIS WOULD PROVIDE A BRIEF WINDOW OF OPPORTUNITY FOR
 MORE SIGNIFICANT DEVELOP THAN CURRENTLY INDICATED. THE OFFICIAL
 FORECAST CALLS FOR FIONA TO MAINTAIN ITS CURRENT INTENSITY FOR THE
 NEXT 48 HOURS...ALTHOUGH THERE MAY SOME FLUCTUATIONS DURING THAT
 TIME AS THE SHEAR WAXES AND WANES. THIS SCENARIO IS CONSISTENT WITH
 THE GFDL AND HWRF MODELS.
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      02/0900Z 22.6N  65.4W    45 KT
  12HR VT     02/1800Z 24.6N  66.6W    45 KT
  24HR VT     03/0600Z 27.1N  67.3W    45 KT
  36HR VT     03/1800Z 29.7N  67.0W    45 KT
  48HR VT     04/0600Z 32.4N  65.8W    45 KT
  72HR VT     05/0600Z 36.5N  62.0W    35 KT
  96HR VT     06/0600Z...DISSIPATED
  
 $$
 FORECASTER STEWART
  
 
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