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| #57698 (Received by flhurricane at: 3:43 AM 20.Nov.2005) TCDAT2 TROPICAL STORM GAMMA DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 4 AM EST SUN NOV 20 2005 EARLIER DEEP CONVECTIVE BURSTS NEAR AND TO THE NORTHEAST OF THE CENTER HAVE WEAKENED CONSIDERABLY DURING THE PAST 6 HOURS. THE HIGHEST 1500 FT FLIGHT-LEVEL WINDS INDICATED BY AN AIR FORCE RESERVE RECON AIRCRAFT HAS BEEN 37 KT IN A FEW SPOTS JUST NORTH AND NORTHEAST OF THE CENTER... WHICH DOES NOT SUPPORT TROPICAL STORM STATUS. AT BEST...GRADIENT WIND COMPUTATIONS SUPPORT BORDERLINE TROPICAL STORM-FORCE WINDS SOMEWHERE IN THE NORTHERN SEMICIRCLE. SINCE WHAT CONVECTION REMAINS IS LOCATED BETWEEN THE FLIGHT LEGS IN THE NORTHEAST QUADRANT... GAMMA IS BEING KEPT A TROPICAL STORM BUT THE WINDS HAVE BEEN LOWERED TO 35 KT... WHICH MAY BE GENEROUS. THE INITIAL MOTION IS 360/02...BASED ON A 12-HOUR MOTION. THE LAST SEVERAL RECON POSITONS INDICATE GAMMA HAS ONLY DRIFTED SLOWLY NORTHWARD. UPPER-AIR DATA AT 00Z ALONG WITH DROPSONDE DATA FROM THE NOAA G-IV JET AIRCRAFT SHOW A WEAKNESS OVER WESTERN CUBA AND THE YUCATAN CHANNEL STILL EXISTS WITHIN THE MID-LEVEL RIDGE LOCATED TO THE NORTH... BUT THE LOW-LEVEL RIDGE HAS REMAINED INTACT. MODERATE TO STRONG SOUTHERLY UPPER-LEVEL WIND FLOW HAS HELPED TO MAINTAIN A SHEARING PATTERN ACROSS GAMMA. THE RESULT IS THAT THE CYCLONE NOW APPEARS TO BE VERTICALLY LESS DEEP THAN THIS TIME YESTERDAY... AND THE SYSTEM MAY NOT EVEN BE AROUND AS A TROPICAL CYCLONE IN 48 HOURS ACCORDING TO THE SHIPS MODEL. THE VARIOUS NHC TRACK MODELS MOVE A WEAKENING GAMMA EAST-NORTHEASTWARD TO SOUTHEASTWARD THROUGH THE FORECAST PERIOD... WITH SEVERAL OF THE MODELS FORECASTING DISSIPATION OR ABSORPTION BY 96 HOURS AS A STRONG COLD FRONT PUSHES INTO THE CARIBBEAN SEA. THE OFFICIAL TRACK WAS SHIFTED WELL SOUTH OF THE PREVIOUS TRACK AND AGREES WITH THE CONSENSUS OF THE GLOBAL MODELS WITH EITHER DISSIPATION OR ABSORPTION OCCURRING BY 72-96 HOURS OVER THE WEST-CENTRAL CARIBBEAN SEA. ADDITONAL STRENGTHENING APPEARS UNLIKELY DUE TO INCREASING VERTICAL SHEAR AND MID-LEVEL DRY AIR ENTRAINMENT FROM THE SOUTH. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 20/0900Z 16.7N 85.0W 35 KT 12HR VT 20/1800Z 17.1N 85.3W 35 KT 24HR VT 21/0600Z 17.5N 85.0W 30 KT 36HR VT 21/1800Z 17.9N 84.0W 30 KT 48HR VT 22/0600Z 18.0N 82.2W 25 KT...DISSIPATING 72HR VT 23/0600Z 17.5N 78.0W 25 KT...DISSIPATING 96HR VT 24/0600Z...ABSORBED BY FRONTAL SYSTEM |
