Tropical Storm GAMMA

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TROPICAL STORM GAMMA DISCUSSION NUMBER  16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
4 PM EST SAT NOV 19 2005
 
VISIBLE IMAGERY AND REPORTS FROM AN AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT INDICATE THAT THE CENTER OF GAMMA IS 30 N MI OR
MORE SOUTHEAST OF THE LOCATION OF THE PREVIOUS TWO ADVISORIES. 
SATELLITE IMAGERY SHOWS THAT THE CENTER IS EXPOSED TO THE SOUTH OF
THE MAIN CONVECTIVE MASS...WHICH APPEARS RAGGED AND DISORGANIZED. 
HOWEVER...THE HURRICANE HUNTER REPORTED A CENTRAL PRESSURE OF 1004
MB AND FLIGHT LEVEL WINDS OF 49 KT AT 1500 FT 25-30 N MI NORTHWEST
OF THE CENTER.  BASED ON THE AIRCRAFT DATA...THE INITIAL INTENSITY
REMAINS 40 KT.

THE INITIAL MOTION IS A VERY UNCERTAIN 360/2 BASED ON 24 HR OF
MOTION.  HOWEVER...THE LATEST SATELLITE IMAGERY SUGGESTS A
SHORT-TERM EASTWARD DRIFT.  GAMMA IS CURRENTLY IN AN AREA OF WEAK
STEERING CURRENT SOUTH OF A LOW-LEVEL RIDGE OVER THE GULF OF MEXICO
AND BETWEEN SEGMENTS OF A MID-LEVEL RIDGE.  THE LARGE-SCALE MODELS
CONTINUE TO FORECAST THE RIDGES TO BREAK DOWN AS A DEEP-LAYER
TROUGH AND SURFACE LOW DEVELOP OVER THE EASTERN UNITED STATES AND
ADJACENT WATERS DURING THE NEXT 2-3 DAYS.  THIS DEVELOPMENT SHOULD
TURN GAMMA MORE NORTHEASTWARD WITH TIME.  THE GFDL CONTINUES TO
BRING A STRONGER GAMMA TO THE NORTH OF THE OTHER MODELS...ALTHOUGH
IT HAS SHIFTED SOUTHWARD ON ITS LATEST RUN.  THE GFS AND UKMET CALL
FOR A MORE EASTWARD MOTION ACROSS THE NORTHWESTERN CARIBBEAN.  DUE
TO THE MODEL TRENDS ALONG WITH THE CURRENT POSITION AND MOTION...
THE NEW FORECAST TRACK HAS CHANGED CONSIDERABLY FROM THE PREVIOUS
TRACK...CALLING FOR GAMMA TO MOVE GENERALLY NORTHWARD FOR 24-36 HR
FOLLOWED BY A TURN TOWARD THE NORTHEAST WITH SOME ACCELERATION
TOWARD CENTRAL CUBA.  THIS TRACK IS WELL SOUTHEAST OF THE PREVIOUS
TRACK...AND CALLS FOR LESS ACCELERATION AFTER 36 HR.  THIS IS STILL
A SOMEWHAT UNCERTAIN FORECAST...AND ADDITIONAL CHANGES TO THE TRACK
COULD OCCUR TONIGHT BASED ON DATA FROM THE FLIGHT OF THE NOAA G4
JET CURRENTLY UNDERWAY.
 
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOWS 20-30 KT OF
SOUTHWESTERLY VERTICAL SHEAR OVER GAMMA.  EVEN WITH A MORE
SOUTHERLY FORECAST TRACK THAN 6 HR AGO...THE LARGE-SCALE MODELS
CONTINUE TO FORECAST THE SHEAR TO INCREASE...WHICH WILL ALLOW
LITTLE IF ANY STRENGTHENING.  ALSO...REGARDLESS OF THE EXACT
TRACK...THE COLD FRONT ASSOCIATED WITH THE BAROCLINIC LOW WILL BE
STRONG ENOUGH TO SWEEP WELL INTO THE CARIBBEAN AND CATCH GAMMA. 
BASED ON THESE TWO PREMISES...THE INTENSITY FORECAST WILL HOLD THE
INTENSITY AT 40 KT UNTIL 72 HR...WHEN GAMMA SHOULD BE MERGING WITH
THE FRONT.  THE BAROCLINIC LOW SHOULD ABSORB GAMMA BY 96 HR.  AN
ALTERNATIVE SCENARIO IS THAT THE SHEAR COULD WEAKEN GAMMA EVEN
BEFORE THE FRONT CATCHES IT.
 
FORECASTER BEVEN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/2100Z 16.3N  85.2W    40 KT
 12HR VT     20/0600Z 16.8N  85.2W    40 KT
 24HR VT     20/1800Z 17.8N  85.1W    40 KT
 36HR VT     21/0600Z 18.9N  84.8W    40 KT
 48HR VT     21/1800Z 20.7N  83.2W    40 KT
 72HR VT     22/1800Z 23.0N  76.0W    35 KT...BECOMING EXTRATROPICAL
 96HR VT     23/1800Z...ABSORBED BY EXTRATROPICAL LOW
 
 
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