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| #372936 (Received by flhurricane at: 5:06 PM 01.Sep.2010) 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 |
