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| #57599 (Received by flhurricane at: 9:55 AM 19.Nov.2005) TCDAT2 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 |
