Tropical Storm GAMMA

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TROPICAL DEPRESSION GAMMA DISCUSSION NUMBER  19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
10 AM EST SUN NOV 20 2005
 
CONVECTION HAS SIGNIFICANTLY WANED DURING THE PAST 6 HOURS WITH THE
CLOSEST DEEP CONVECTION LOCATED A COUPLE HUNDRED MILES TO THE
NORTHEAST OF THE NOW FULLY EXPOSED LOW-LEVEL CENTER. ANOTHER WEAK
BAND OF CONVECTION HAS RECENTLY DEVELOPED SOUTHEAST OF THE CENTER
ALONG THE HONDURAS COAST... BUT IT IS NOT SHOWING ANY SIGNS AT THIS
TIME OF TRYING TO WRAP INTO THE CENTER. SATELLITE ESTIMATES HAVE
DECREASED ACCORDINGLY... SO THE INITIAL INTENSITY IS SET TO 30 KT
...BASED MAINLY ON THE TIGHT SWIRL NOTED IN THE LOW-LEVEL CLOUDS.
 
THE INITIAL MOTION IS 325/03... ALTHOUGH GAMMA APPEARS TO BE MAKING
A SMALL COUNTER-CLOCKWISE LOOP. UPPER-AIR DATA AT 12Z INDICATE
LITTLE CHANGE TO THE OVERALL STEERING FLOW PATTERN... EXCEPT THAT
THE BREAK IN THE 500 MB RIDGE TO THE NORTH HAS FILLED IN. THIS
SHOULD HELP TO KEEP GAMMA TRAPPED IN THE NORTHWESTERN CARIBBEAN FOR
THE NEXT FEW DAYS UNTIL A STRONG COLD FRONT CAPTURES THE CYCLONE BY
72 HOURS. THE NOGAPS...GFDN... AND COAMPS MODELS MAINTAIN A DEEPER
AND STRONGER CIRCULATION THAN DO THE REST OF THE NHC MODELS...WHICH
SEEMS UNREASONABLE BASED ON THE 12Z BELIZE SOUNDING. IN CONTRAST...
THE GFS AND GFS ENSEMBLE MODELS WEAKEN GAMMA OVER THE NEXT COUPLE
OF DAYS AND DRIFT IT AROUND WITHIN 90 NMI OF ITS CURRENT LOCATION.
THE REMAINING MODELS ALSO WEAKEN THE CYCLONE AND DRIFT IT SLOWLY
EAST OR SOUTHEASTWARD. THE OFFICIAL FORECAST TRACK IS SIMILAR TO
THE PREVIOUS TRACK AND LEANS CLOSELY TOWARD THE GFS MODELS... WITH
DISSIPATION POSSIBLY OCCURRING WITHIN 24 HOURS OR LESS.
 
ADDITIONAL WEAKENING APPEARS LIKELY DUE TO INCREASING VERTICAL
SHEAR... AND ENTRAINMENT OF DRY MID-LEVEL AIR FROM CENTRAL AMERICA
AS NOTED IN 12Z UPPER-AIR DATA FROM BELIZE. THE SHIPS MODEL
DISSIPATES GAMMA BY 24 HOURS. THIS RAPID DOWNWARD INTENSITY TREND
WAS CLOSELY FOLLOWED... ESPECIALLY GIVEN THE VERY POOR APPEARANCE
OF GAMMA IN THE MOST RECENT SATELLITE IMAGERY.
 
FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/1500Z 16.9N  85.3W    30 KT
 12HR VT     21/0000Z 17.1N  85.2W    25 KT...DISSIPATING
 24HR VT     21/1200Z 17.5N  84.4W    25 KT...DISSIPATING
 36HR VT     22/0000Z 17.7N  83.0W    20 KT...REMNANT LOW
 48HR VT     22/1200Z 17.7N  81.1W    20 KT...REMNANT LOW
 72HR VT     23/1200Z...MERGED WITH FRONTAL SYSTEM

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