864 
 WTNT42 KNHC 200840
 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
  
 $$