Tropical Storm GAMMA

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TROPICAL STORM GAMMA DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
10 AM EST SAT NOV 19 2005
 
VISIBLE IMAGERY AND RECENT MICROWAVE DATA FROM TRMM AND SSM/I
SUGGEST THAT THE LOW-LEVEL CENTER OF GAMMA IS A LITTLE TO THE
SOUTHEAST OF THE PREVIOUS ADVISORY POSITION...NEAR THE SOUTHERN
EDGE OF THE MAIN CONVECTIVE CLUSTER.  THIS POSITION IS INDICATIVE
OF THE 20-30 KT VERTICAL SHEAR ANALYZED BY THE SHIPS MODEL AND
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN.  SATELLITE
INTENSITY ESTIMATES ARE 45 KT FROM TAFB...AND 35 KT FROM SAB AND
AFWA.  BASED ON THIS...THE INITIAL INTENSITY REMAINS 40 KT.

THE INITIAL MOTION IS A RATHER UNCERTAIN 330/4.  GAMMA IS SOUTH OF A
LOW-LEVEL RIDGE OVER THE SOUTHEASTERN UNITED STATES AND THE EASTERN
GULF OF MEXICO...AND BETWEEN TWO SEGMENTS OF A MID-LEVEL RIDGE. 
LARGE-SCALE MODELS UNANIMOUSLY AGREE THAT THESE RIDGES WILL BREAK
DOWN DURING THE NEXT 48-72 HR AS A STRONG DEEP-LAYER TROUGH CAUSES
A FRONTAL LOW TO FORM OVER FLORIDA OR THE EASTERN GULF OF MEXICO. 
THIS EVOLUTION SHOULD CAUSE GAMMA TO TURN NORTHEASTWARD OR POSSIBLY
EAST-NORTHEASTWARD AS THE SURFACE LOW DEVELOPS.  THE GLOBAL MODELS
CONTINUE TO SHOW A WEAKER GAMMA TURNING MORE EASTWARD ACROSS THE
NORTHWESTERN CARIBBEAN...WHILE THE GFDL WITH ITS STRONGER STORM
CALLS FOR A NORTHEASTWARD MOTION NEAR THE NORTHERN EDGE OF THE
GUIDANCE ENVELOPE.  THE NEW TRACK FORECAST IS CLOSEST TO...BUT
SOUTH OF...THE GFDL...AND IS NUDGED TO THE SOUTHEAST OF THE
PREVIOUS FORECAST BASED ON THE CURRENT POSITION AND MOTION.  THIS
IS STILL A SOMEWHAT UNCERTAIN FORECAST...AND ADDITIONAL CHANGES TO
THE TRACK COULD OCCUR LATER TODAY OR TONIGHT BASED ON DATA FROM THE
FLIGHT OF THE NOAA G4 JET STARTING AT 18Z.
 
GAMMA IS ALREADY UNDER MODERATE TO STRONG SOUTHWESTERLY VERTICAL
SHEAR...AND THE LARGE-SCALE MODELS FORECAST THE SHEAR TO INCREASE
DURING THE NEXT 72 HR.  THIS SHOULD NOT ALLOW GAMMA TO STRENGTHEN
SIGNIFICANTLY.  THE SHIPS MODEL WEAKENS THE SYSTEM...WHILE THE GFDL
CALLS FOR IT TO PEAK AT 60 KT IN ABOUT 48 HR.  THE LATTER MIGHT BE
A BIT OPTIMISTIC IN LIGHT OF THE FORECAST SHEAR.  THE INTENSITY
FORECAST WILL CALL FOR SOME MODEST STRENGTHENING IN THE FIRST 12
HR...THEN KEEP THE INTENSITY AT 45 KT THROUGH THE REST OF THE LIFE
OF THE CYCLONE.  THE BAROCLINIC LOW AND ASSOCIATED COLD FRONT ARE
FORECAST TO BE STRONG ENOUGH THAT...REGARDLESS OF THE EXACT TRACK
OF GAMMA...THEY SHOULD ABSORB GAMMA AFTER 72 HR.

THE RECENT MICROWAVE DATA SUGGEST THAT THE CENTER MIGHT BE A LITTLE
FARTHER SOUTHEAST OF THE NEW ADVISORY POSITION.  IF THIS IS THE
CASE...AN ADDITIONAL RE-LOCATION MAY BE NECESSARY AFTER THE AIR
FORCE RESERVE HURRICANE HUNTER REACHES THE STORM AROUND 18Z.
 
FORECASTER BEVEN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/1500Z 16.8N  85.9W    40 KT
 12HR VT     20/0000Z 17.6N  86.4W    45 KT
 24HR VT     20/1200Z 18.7N  86.4W    45 KT
 36HR VT     21/0000Z 20.0N  85.8W    45 KT
 48HR VT     21/1200Z 21.9N  84.0W    45 KT
 72HR VT     22/1200Z 27.5N  76.0W    45 KT...BECOMING EXTRATROPICAL
 96HR VT     23/1200Z...ABSORBED BY EXTRATROPICAL LOW
 
 
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