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| #211091 (Received by flhurricane at: 10:54 PM 27.Aug.2008) TCDAT2 TROPICAL STORM GUSTAV DISCUSSION NUMBER 12 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008 1100 PM EDT WED AUG 27 2008 THE LAST RECONNAISSANCE FIX WAS AT 23Z. DATA FROM THE AIRCRAFT INDICATED THAT THE CENTER OF GUSTAV BEGAN TO MOVE WEST- SOUTHWESTWARD AND AWAY FROM THE DEEP CONVECTION. PEAK FLIGHT-LEVEL WINDS WERE 39 KT AND THE HIGHEST RECENT BELIEVABLE SFMR WINDS WERE 41 KT. THE ADVISORY INTENSITY IS LOWERED TO 40 KT BASED ON THESE OBSERVATIONS. THE INITIAL MOTION IS NOW ESTIMATED TO BE 250/7...ALTHOUGH THE CENTER HAS BEEN VERY HARD TO TRACK SINCE THE TIME OF THE LAST FIX AND MIGHT BE A LITTLE SOUTH OF MY ADVISORY POSITION. A DEEP-LAYER RIDGE...ORIENTED NORTHEAST-SOUTHWEST...IS CENTERED OVER THE FLORIDA PENINSULA. THIS RIDGE HAS IMPARTED A BIT OF A SOUTHERLY COMPONENT OF MOTION THAT SOME MODELS SHOW PERSISTING FOR ANOTHER 24 HOURS OR SO. AFTER THAT...GUSTAV IS EXPECTED TO ROUND THE PERIPHERY OF THE RIDGE AND TURN TO THE NORTHWEST IN THE EASTERN GULF OF MEXICO. COMPLICATING THE FORECAST IN THE LATTER PART OF THE PERIOD IS THE EVOLUTION AND IMPACT OF AN UPPER-LEVEL TROUGH EXPECTED TO BE IN THE CENTRAL OR WESTERN GULF OF MEXICO...AS WELL AS THE DEVELOPMENT OF A BLOCKING HIGH AT THE END OF THE PERIOD REMINISCENT OF WHAT HAPPENED WITH FAY A WEEK OR SO AGO. GIVEN THESE FACTORS...THE MODEL GUIDANCE IS IN SURPRISINGLY GOOD AGREEMENT. THE OFFICIAL FORECAST RELIES MOST STRONGLY ON A BLEND OF THE ECMWF...UKMET...GFDL...AND GFS...WHICH IS NOW FOLLOWING THE VORTEX FAIRLY WELL...AND IS JUST TO THE LEFT OF THE PREVIOUS ADVISORY TRACK. THE DYNAMICAL MODEL CONSENSUS IS A LITTLE FARTHER TO THE LEFT. GUSTAV HAS BEEN SIGNIFICANTLY DISPRUPTED BY ITS ENCOUNTER WITH THE TERRAIN OF HAITI. IN ADDITION...MID-LEVEL DRY AIR APPEARS TO BE OVERTAKING THE CYCLONE FROM THE NORTHEAST. IN ANOTHER 24-36 HOURS...HOWEVER...GUSTAV SHOULD FIND ITSELF UNDER AN UPPER ANTICYCLONE AND OVER THE VERY DEEP WARM WATERS OF THE NORTHWESTERN CARIBBEAN...AND SO THE CYCLONE SHOULD HAVE AN OPPORTUNITY TO RESTRENGTHEN. IN ADDITION...THE FORECAST TRACK TAKES GUSTAV OVER THE LOOP CURRENT IN THE SOUTHEASTERN GULF. AFTER THAT...GLOBAL MODELS SUGGEST THE POSSIBILITY OF SOUTHWESTERLY SHEAR IN THE GULF ASSOCIATED WITH THE UPPER TROUGH THAT COULD SLOW THE INTENSIFICATION RATE. THE OFFICIAL FORECAST SHOWS A SLOWER RESTRENGTHENING THAN THE PREVIOUS ADVISORY INITIALLY...BUT IS OTHERWISE SIMILAR...AND ROUGHLY SPLITS THE DIFFERENCE BETWEEN THE SHIPS AND GFDL GUIDANCE. IT PROBABLY WOULDN'T HURT TO REMIND EVERYONE THAT THE AVERAGE 5-DAY OFFICIAL TRACK ERROR IS ABOUT 300 MILES...AND THE AVERAGE 5-DAY INTENSITY ERROR IS ABOUT 25 MPH. FORECAST POSITIONS AND MAX WINDS INITIAL 28/0300Z 18.8N 75.4W 40 KT 12HR VT 28/1200Z 18.8N 76.5W 45 KT 24HR VT 29/0000Z 18.9N 78.0W 50 KT 36HR VT 29/1200Z 19.4N 79.5W 60 KT 48HR VT 30/0000Z 20.1N 81.0W 70 KT 72HR VT 31/0000Z 22.5N 84.5W 85 KT 96HR VT 01/0000Z 26.0N 87.5W 95 KT 120HR VT 02/0000Z 29.0N 89.5W 95 KT $$ FORECASTER FRANKLIN |
