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| #57486 (Received by flhurricane at: 3:46 PM 18.Nov.2005) TCDAT2 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 |
