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| #57635 (Received by flhurricane at: 3:34 PM 19.Nov.2005) TCDAT2 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 |
