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| #25537 (Received by flhurricane at: 11:00 PM 09.Jun.2005) TCDAT1 TROPICAL STORM ARLENE DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT THU JUN 09 2005 SATELLITE IMAGERY AND RECON DATA INDICATE THAT ARLENE HAS CHANGED LITTLE OVER THE PAST 6 HOURS. RECON REPORTED 1500 FT WIND OF 46 KT IN THE NORTHEAST QUADRANT AROUND 2115Z...BUT A SUBSEQUENT PASS THROUGH THE SAME AREA REVEALED ONLY 32 KT WINDS. SINCE THE CONVECTION HAS WEAKENED SOME AND BECOME A LITTLE RAGGED...THE INTENSITY IS BEING MAINTAINED AT 35 KT. HI-RES VISIBLE SATELLITE IMAGERY AND RECON DATA INDICATE MULTIPLE SMALL CIRCULATIONS HAVE BEEN ROTATING AROUND INSIDE A LARGER WELL-DEFINED OUTER CYCLONIC ENVELOPE. THE INITIAL POSITION IS AN AVERAGE OF THESE VORTEX POSITIONS AND VERY CLOSE TO A 09/2324Z QUIKSCAT CENTER POSITION. THE INITIAL MOTION ESTIMATE IS 350/07. THE AFOREMENTIONED QUIKSCAT POSITION WOULD SUGGEST THAT ARLENE MAY BE A LITTLE FARTHER WEST... BUT I HAVE OPTED TO STAY CLOSER TO WHAT DEEP CONVECTION EXISTS AND WITHIN THE RECON VORTEX ENVELOPE. NHC MODEL GUIDANCE REMAINS IN STRONG AGREEMENT ON ARLENE MOVING ACROSS WESTERN CUBA TONIGHT AND THEN TURNING NORTH-NORTHWESTWARD OVER THE SOUTHEASTERN GULF OF MEXICO ON FRIDAY. THIS ANTICIPATED TURN IS IN RESPONSE TO THE CYCLONE BEGINNING TO FEEL THE INFLUENCE OF A BUILDING RIDGE ACROSS THE WESTERN ATLANTIC...SOUTHEASTERN U.S....AND THE FLORIDA PENINSULA. ONE CONCERN IS THE UPPER-LEVEL OUTFLOW IN THE EASTERN SEMICIRCLE IS FORECAST TO GET PINCHED BETWEEN DIGGING TROUGHS OVER THE WESTERN GULF AND ALSO OVER THE CENTRAL ATLANTIC. THIS TYPE OF BLOCKING PATTERN OFTENTIMES RESULTS IN THE LOW- TO MID-LEVEL RIDGE BEING STRONGER...WHICH WOULD HELP TO NUDGE ARLENE A LITTLE MORE WESTWARD. THE OFFICIAL FORECAST IS JUST AN EXTENSION OF THE PREVIOUS FORECAST TRACK. MID-LEVEL DRY AIR NOTED IN WATER VAPOR IMAGERY AND NOAA G-IV JET AIRCRAFT DATA HAS BEEN PUNCHING INTO THE CENTER FROM THE SOUTHWEST AND HAS TEMPORARILY ERODED MOST OF THE CONVECTION. HOWEVER...THE DRY AIR ENTRAINMENT IS EXPECTED TO DECREASE AS THE MID- TO UPPER-LEVEL FLOW GRADUALLY BACKS AROUND TO THE SOUTH-SOUTHEAST... WHICH WILL BE ALONG THE FORECAST TRACK. THE GFDL BRINGS ARLENE UP 63 KT JUST BEFORE LANDFALL WHILE THE SHIPS MODEL ONLY STRENGTHENS THE CYCLONE TO 45 KT. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THESE MODELS. HOWEVER...GIVEN THAT THE UPPER-LEVEL FLOW IS FORECAST TO DECREASE TO LESS THAN 15 KT WHILE CONTINUING TO BACK...AND THAT SSTS ARE EXPECTED TO BE 28-29C UNTIL LANDFALL BASED ON CURRENT BUOY OBSERVATIONS...ARLENE COULD PEAK A LITTLE STRONGER BETWEEN 36-48 HOURS BEFORE WEAKENING BEGINS WHEN UPPER-LEVEL SHEAR INCREASES FROM THE SOUTHWEST AS THE CYCLONE NEARS THE U.S. GULF COAST. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 10/0300Z 20.8N 84.3W 35 KT 12HR VT 10/1200Z 22.6N 85.0W 40 KT 24HR VT 11/0000Z 25.0N 86.3W 45 KT 36HR VT 11/1200Z 27.7N 87.9W 50 KT 48HR VT 12/0000Z 30.5N 88.6W 55 KT...NEAR MS/AL COAST 72HR VT 13/0000Z 36.0N 87.0W 20 KT...DISSIPATING INLAND 96HR VT 14/0000Z 41.0N 82.5W 15 KT...REMNANT LOW INLAND 120HR VT 15/0000Z...DISSIPATED INLAND |
