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| #210879 (Received by flhurricane at: 11:08 PM 26.Aug.2008) TCDAT2 TROPICAL STORM GUSTAV DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008 1100 PM EDT TUE AUG 26 2008 BETWEEN 21Z AND 01Z THIS EVENING...RADAR IMAGERY FROM THE CUBAN RADAR SITE AT GRAN PIEDRA DEPICTED A NICE DOUGHNUT SHAPED MID- TO UPPER-LEVEL EYE FEATURE ALONG THE NORTH COAST OF THE SOUTHWESTERN PENINSULA OF HAITI. HOWEVER...SINCE THAT TIME BOTH RADAR AND SATELLITE DATA INDICATE THE EYE FEATURE HAS DEGENERATED INTO A RAGGED AND POORLY DEFINED FEATURE. THEREFORE...GUSTAV HAS BEEN DOWNGRADED TO A TROPICAL STORM AND THE INTENSITY LOWERED TO 60 KT...WHICH IS ONLY SLIGHTLY BELOW THE T4.0/65 KT SATELLITE INTENSITY ESTIMATES DERIVED AT 00Z. UPPER-LEVEL OUTFLOW IS SLIGHTLY RESTRICTED BUT IMPROVING IN THE NORTHWESTERN QUADRANT... AND IS EXCELLENT IN THE OTHER THREE QUADRANTS. THE AVERAGE MOTION OVER THE PAST 6 HOURS IS 290/07...ALTHOUGH THE MOTION OVER THE PAST 3 HOURS HAS BEEN ALMOST DUE WEST. THE PRIMARY STEERING MECHANISM FOR THE NEXT 5 DAYS WILL BE THE LARGE MID- TO UPPER-LEVEL ANTICYCLONE CENTERED OVER THE FLORIDA STRAITS...WHICH IS FORECAST TO AMPLIFY NORTHWARD OVER THE SOUTHEASTERN U.S. AND AN UPPER-LEVEL TROUGH OVER THE NORTHWESTERN GULF IS ALSO EXPECTED TO BE A PLAYER AND ACT TO SLOW DOWN GUSTAV BY DAY 5. THE EXCEPTIONS ARE THE GFDL AND ECMWF MODELS...WHICH BLAST GUSTAV NORTHWESTWARD THROUGH THE UPPER-TROUGH TO THE TEXAS COAST. THIS SEEMS PHYSICALLY UNLIKELY AT THIS JUNCTURE. THE OFFICIAL FORECAST CALLS FOR GUSTAV TO GRADUALLY MOVE AROUND THE SOUTHERN PERIPHERY OF THE MID-LEVEL RIDGE TO THE NORTH AND MOVE OUT INTO THE CENTRAL GULF OF MEXICO BY DAYS 4 AND 5. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE PREVIOUOS ADVISORY TRACK...AND REMAINS ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE IN THE EXPECTATION THAT THE SOUTHWESTERLIES ASSOCIATED WITH THE UPPER TROUGH WILL PLAY A MORE PROMINENT ROLE THAN INDICATED BY THE GFDL AND ECMWF. GUSTAV IS ON THE EAST SIDE OF A LARGE UPPER-LEVEL ANTICYCLONE... WHICH IS INDUCING SOME LIGHT NORTHERLY SHEAR ON THE CYCLONE. HOWEVER...THE FLOW IS ALSO STRONGLY DIFLUENT...WHICH SHOULD AID THE RE-INTENSIFICATION PROCESS ONCE GUSTAV CLEARS THE WESTERN PORTION OF HAITI. BOTH THE UPPER-LEVEL FLOW AND OCEANIC CONDITIONS OVER THE NORTHWESTERN CARIBBEAN BETWEEN 36 AND 72 HOURS ARE EXPECTED TO BE CONDUCIVE FOR SIGNIFICANT INTENSIFICATION TO OCCUR...AND THIS IS REFLECTED IN THE OFFICIAL FORECAST BY BRINGING GUSTAV TO JUST BELOW CATEGORY 4 STRENGTH BY 72 HOURS. AFTER THAT...POSSIBLE EYEWALL REPLACEMENT CYCLES AND SOUTHWESTERLY WIND SHEAR MAY CREATE INTENSITY FLUCTUATIONS IN THE LATTER FORECAST PERIODS. FORECAST POSITIONS AND MAX WINDS INITIAL 27/0300Z 18.6N 73.6W 60 KT 12HR VT 27/1200Z 18.9N 74.5W 65 KT 24HR VT 28/0000Z 19.0N 75.7W 75 KT 36HR VT 28/1200Z 19.2N 77.1W 85 KT 48HR VT 29/0000Z 19.4N 78.5W 95 KT 72HR VT 30/0000Z 20.5N 82.2W 110 KT 96HR VT 31/0000Z 23.0N 86.0W 110 KT 120HR VT 01/0000Z 26.5N 89.5W 110 KT $$ FORECASTER STEWART/FRANKLIN |
