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| #372862 (Received by flhurricane at: 5:04 AM 01.Sep.2010) TCDAT3 TROPICAL STORM FIONA DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082010 500 AM AST WED SEP 01 2010 RECONNAISSANCE DATA...RADAR DATA FROM GUADELOUPE...AND SATELLITE IMAGERY INDICATE FIONA HAS BECOME A LITTLE BETTER ORGANIZED THIS MORNING. DEEP CONVECTION HAS INCREASED IN THE SOUTHERN SEMICIRCLE AND THE CENTER HAS BECOME BETTER DEFINED IN RADAR IMAGERY AND IN FLIGHT-LEVEL WIND DATA. THE MAXIMUM 850 MB FLIGHT-LEVEL WINDS OBSERVED THUS FAR DURING THE CURRENT MISSION HAS BEEN 52 KT IN THE NORTHEAST QUADRANT...WHICH EQUATES TO ABOUT A 42-KT SURFACE WIND. THE LOWEST PRESSURES OBSERVED THUS FAR HAVE BEEN 1002 MB AT 0602Z AND 1004 MB AT 0803Z. THE INITIAL INTENSITY IS SET AT 40 KT...WHICH IS LOWER THAN THE 50-KT ADT INTENSITY ESTIMATE FROM UW-CIMSS. THE INITIAL MOTION IS 290/12 KT USING RECON AND RADAR FIX POSITIONS. FIONA APPEARS TO HAVE DECREASED ITS RATE OF CLOSURE ON EARL LOCATED TO ITS NORTHWEST. OVER THE PAST 48 HOURS...THE DISTANCE BETWEEN FIONA AND EARL HAS BEEN DECREASING BY ABOUT 100 NMI EVERY 12 HOURS...AND THE TWO CYCLONES ARE CURRENTLY ABOUT 750 NMI APART. RIDDING BETWEEN THE TWO SYSTEMS HAS OBVIOUSLY INCREASED...WHICH HAS RESULTED IN THE SIGNIFICANT DECREASE IN THE FORWARD SPEED OF FIONA FROM MORE THAN 20 KT DOWN TO THE CURRENT 12 KT IN THE PAST 12 HOURS. THE POSSIBLE CAUSE OF THE RIDGING TO THE NORTHWEST OF FIONA IS THE UPPER-LEVEL OUTFLOWS FROM BOTH CYCLONES CONVERGING TO THE NORTHWEST OF FIONA. THIS RIDGING MAY ALLOW KEEP FIONA FROM INTERACTING WITH THE LARGER CIRCULATION OF EARL LIKE MOST OF THE GLOBAL MODELS HAVE BEEN FORECASTING THE PAST COUPLE OF DAYS. ALL OF THE MODEL GUIDANCE...EXCLUDING NOGAPS...NOW SLOWS DOWN FIONA BY DAY 3...WITH THE CYCLONE POSSIBLY GETTING TRAPPED IN THE SUBTROPICAL RIDGE. AS RESULT OF THESE NEW SCENARIO...A 96-HOUR POSITION HAS BEEN ADDED AND DISSIPATION HAS BEEN DELAYED UNTIL 120 HOURS. IF FIONA BECOMES A STRONGER SYSTEM THAN CURRENTLY FORECAST...THE CYCLONE COULD SURVIVE AND END UP MAKING A CLOCKWISE LOOP OR EVEN BECOME STATIONARY BY 120 HOURS. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY..EXCEPT SLOWER AT 48 HOURS AND BEYOND...AND IS ALONG THE WESTERN EDGE OF THE GUIDANCE SUITE. SOME DRY MID-LEVEL AIR APPEARS TO BE GETTING DRAWN INTO THE NORTHERN QUADRANT OF THE FIONA...WHICH MAY BE RESPONSIBLE FOR THE LACK OF SIGNIFICANT CONVECTION IN THAT REGION. HOWEVER...UPPER-LEVEL OUTFLOW HAS IMPROVED SOME AND BECOME A LITTLE MORE CIRCULAR IN APPEARANCE. THE OFFICIAL INTENSITY FORECAST WAS NUDGED UPWARD SLIGHTLY FROM THE PREVIOUS ADVISORY...BUT IS LOWER THAN THE SHIPS AND LGEM MODELS WHICH BRING FIONA UP TO A 60-KT SYSTEM BY 48 HOURS...AND MUCH LOWER THAN THE GFDL MODEL WHICH MAKES FIONA AN 85-KT HURRICANE AT THAT SAME TIME. FORECAST POSITIONS AND MAX WINDS INITIAL 01/0900Z 17.4N 60.2W 40 KT 12HR VT 01/1800Z 18.9N 62.5W 45 KT 24HR VT 02/0600Z 21.2N 64.7W 50 KT 36HR VT 02/1800Z 23.5N 66.5W 50 KT 48HR VT 03/0600Z 26.3N 67.3W 40 KT 72HR VT 04/0600Z 29.2N 67.5W 35 KT 96HR VT 05/0600Z 31.5N 67.0W 30 KT 120HR VT 06/0600Z...DISSIPATED $$ FORECASTER STEWART |
