Tropical Storm GAMMA

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TROPICAL STORM GAMMA DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
3 PM CST FRI NOV 18 2005
 
SURFACE OBSERVATIONS AND REPORTS FROM AN AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT SHOW THAT THE REMNANTS OF TROPICAL DEPRESSION
TWENTY-SEVEN HAVE REFORMED INTO A BROAD CIRCULATION ELONGATED
NORTHEAST TO SOUTHWEST.  THE AIRCRAFT REPORTED MAXIMUM FLIGHT LEVEL
WINDS OF 49 KT AT 1500 FT JUST NORTH OF ROATAN ISLAND...ALONG WITH
TWO SPOTS OF 45 KT WINDS NORTH OF THE CENTER.  BASED ON THIS...
ADVISORIES ARE RE-INITIATED ON THIS SYSTEM AS TROPICAL STORM GAMMA
WITH 35 KT WINDS.  WHILE SATELLITE IMAGERY SHOWS THE CYCLONE IS
SLOWLY GETTING BETTER ORGANIZED...THE CONVECTIVE TOPS NEAR THE
CENTER HAVE WARMED DURING THE PAST SEVERAL HOURS.  THE CIRRUS
OUTFLOW IS GOOD IN THE NORTH SEMICIRCLE AND POOR TO RESTRICTED
ELSEWHERE.

THE INITIAL MOTION IS A VERY UNCERTAIN 300/04...WITH ADDITIONAL
UNCERTAINTY ADDED BY THE ELONGATION OF THE CENTER.  GAMMA IS 
CURRENTLY SOUTH OF A WEAK MID-LEVEL RIDGE OVER THE NORTHWESTERN
CARIBBEAN AND A STRONG LOW-LEVEL RIDGE OVER THE GULF OF MEXICO
BEHIND A COLD FRONT EXTENDING FROM SOUTH FLORIDA TO THE YUCATAN
PENINSULA.  THE LARGE-SCALE MODELS UNANIMOUSLY FORECAST THESE
RIDGES TO WEAKEN DURING THE NEXT 72 HR AS A STRONG SHORTWAVE TROUGH
MOVES INTO THE SOUTHEASTERN UNITED STATES...ACCOMPANIED BY SURFACE
CYCLOGENESIS OVER EITHER THE EASTERN GULF OF MEXICO OR THE ATLANTIC
OCEAN OFF THE SOUTHEASTERN U. S. COAST.  THIS PATTERN EVOLUTION
SHOULD TURN GAMMA NORTHWARD AND THEN ACCELERATE NORTHEASTWARD. 
WHILE THERE IS AGREEMENT ON THE PATTERN...THERE IS LITTLE AGREEMENT
BETWEEN THE MODELS ON THE TRACK OF GAMMA...AS MOST OF THE GLOBAL
MODELS FORECAST DISSIPATION IN 72 HR OR LESS.  THE GFS AND NOGAPS
FORECAST A VERY WEAK GAMMA TO TURN EASTWARD ACROSS THE CARIBBEAN...
WHILE THE GFDL BRINGS A STRONGER GAMMA TOWARD SOUTH FLORIDA.  THE
OFFICIAL FORECAST TRACK LEANS MORE ON THE GFDL ON THE BASIS THAT IT
HAS A STRONGER SYSTEM MORE IN LINE WITH THE INTENSITY FORECAST. 
HOWEVER...IF GAMMA DOES NOT HOLD TOGETHER AS WELL AS FORECAST THE
MOTION COULD BE MORE IN LINE WITH THE GFS AND NOGAPS.

GAMMA IS IN A RATHER HOSTILE ENVIRONMENT AT THIS TIME.  SHEAR
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOW 15-25 KT OF
SHEAR ACROSS THE STORM...AND LARGE-SCALE MODELS FORECAST THE SHEAR
TO INCREASE SIGNIFICANTLY OVER THE NEXT 72 HR.  IN ADDITION...GAMMA
IS CLOSE TO A FRONTAL ZONE...AND THE FRONT WILL LIKELY BECOME
STRONGER AS THE SHORTWAVE TROUGH APPROACHES.  THE GFDL MODEL CALLS
FOR GAMMA TO REACH 55 KT IN ABOUT 72 HR...WHILE THE SHIPS MODEL
BARELY STRENGTHENS IT DUE TO SHEAR.  THE INTENSITY FORECAST FOLLOWS
THE GFDL GUIDANCE AND CALL FOR A 55 KT INTENSITY IN 72 HR...
ALTHOUGH GIVEN THE STRENGTH OF THE SHEAR THIS MIGHT BE GENEROUS. 
AFTER 72 HR...GAMMA SHOULD RAPIDLY LOSE TROPICAL CHARACTERISTICS
AND ITS IDENTITY AS IT IS ABSORBED INTO THE STRONG BAROCLINIC LOW
OVER THE WESTERN ATLANTIC.  IT SHOULD BE NOTED THAT THE COLD FRONT
ASSOCIATED WITH THE BAROCLINIC LOW SHOULD BE STRONG ENOUGH TO SWEEP
INTO THE CARIBBEAN SEA...SO EVEN IF GAMMA TAKES A MORE EASTWARD
TRACK AS FORECAST BY THE GFS AND NOGAPS THE FRONT WILL STILL
PROBABLY CATCH UP WITH THE STORM.
 
FORECASTER BEVEN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/2100Z 16.4N  85.6W    35 KT
 12HR VT     19/0600Z 16.8N  86.1W    40 KT
 24HR VT     19/1800Z 17.3N  86.8W    45 KT
 36HR VT     20/0600Z 18.2N  87.1W    50 KT
 48HR VT     20/1800Z 20.0N  86.5W    55 KT
 72HR VT     21/1800Z 25.0N  82.0W    55 KT
 96HR VT     22/1800Z 35.0N  71.0W    50 KT...BECOMING EXTRATROPICAL
120HR VT     23/1800Z...ABSORBED BY EXTRATROPICAL LOW
 
 
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