Tropical Storm GAMMA

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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
 
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