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| #202321 (Received by flhurricane at: 5:08 PM 21.Jul.2008) TCDAT4 TROPICAL STORM DOLLY DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042008 500 PM EDT MON JUL 21 2008 THE STRUCTURE OF DOLLY APPEARS TO BE UNDERGOING VERY GRADUAL CHANGES. THE OUTERMOST CONVECTIVE BANDS HAVE BEEN WEAKENING TODAY...WHILE CONVECTION HAS BEEN SLOWLY ON THE INCREASE NEAR THE CIRCULATION CENTER. THE RADIUS OF MAXIMUM WINDS IS NOW MUCH SMALLER...AS DETERMINED FROM STEPPED-FREQUENCY MICROWAVE RADIOMETER DATA THAT RECENTLY INDICATED A MAXIMUM SURFACE WIND OF 45 KT ABOUT 45 N MI NORTHEAST OF THE CENTER. DOLLY IS HEADED TOWARD A RELATIVE MAXIMUM IN OCEAN HEAT CONTENT...AND IT IS BENEATH A LARGE UPPER-LEVEL ANTICYCLONE THAT COVERS NEARLY THE ENTIRE GULF OF MEXICO. IT SEEMS TO BE TAKING A WHILE...HOWEVER...FOR AN INNER CORE TO BEGIN TO TAKE SHAPE...SO IT IS RATHER UNCERTAIN HOW MUCH DOLLY WILL TAKE ADVANTAGE OF ITS ENVIRONMENT. ALL OF THE INTENSITY MODELS FORECAST AN UPWARD INTENSITY TREND UNTIL FINAL LANDFALL...BUT THEY DO NOT AGREE ON THE AMOUNT OF STRENGTHENING. THE SHIPS AND LGEM MODELS FORECAST ABOUT 65 KT IN 48 HOURS...WHILE THE GFDL IS A LITTLE HIGHER AT 75-80 KT. SINCE THE ENVIRONMENT APPEARS SO CONDUCIVE FOR STRENGTHENING...THE OFFICIAL FORECAST AGAIN LEANS TOWARD THE HIGHER GFDL SOLUTION. ANOTHER COMPLICATION IN THE INTENSITY FORECAST IS NOT KNOWING EXACTLY HOW FAST DOLLY WILL REACH THE COAST. IF IT MAKES LANDFALL SOONER THAN THE OFFICIAL TRACK INDICATES...IT MIGHT RUN OUT OF TIME TO REACH THE OFFICIAL FORECAST PEAK INTENSITY. BUT IF THE OPPOSITE OCCURS...DOLLY WOULD HAVE A LITTLE MORE TIME OVER THE WARM WATERS. DOLLY CONTINUES TO MOVE QUICKLY...AND THE INITIAL MOTION ESTIMATE REMAINS 300/16. WHILE IT IS A LITTLE UNNERVING TO OBSERVE THIS FAST MOTION AND FORECAST THE CENTER OF DOLLY TO TAKE A COUPLE OF DAYS TO REACH THE COAST...ALL OF THE DYNAMICAL MODELS INSIST THAT THE FORWARD SPEED WILL BE ABOUT HALF ITS CURRENT VALUE BY TOMORROW NIGHT. THE MODELS AGREE SURPRISINGLY WELL ON THE SLOW-DOWN...SO THE OFFICIAL TRACK FORECAST...IN TERMS OF FORWARD SPEED...IS RIGHT IN LINE WITH THE MODEL CONSENSUS. THE MODELS DO NOT GO INLAND IN EXACTLY THE SAME LOCATIONS...HOWEVER. THE GFS AND UKMET FORECAST DOLLY TO CROSS THE COAST OF NORTHEASTERN MEXICO...WHILE THE GFDL AND HWRF TRACKS GO INTO SOUTHERN TEXAS. THE OFFICIAL TRACK FORECAST IS A LITTLE NORTH OF THE CONSENSUS...GIVING RESPECT TO THE AGREEMENT BETWEEN THE NWS HURRICANE MODELS...THE GFDL AND HWRF. THIS NEW TRACK IS NOT MEANINGFULLY DIFFERENT THAN THE PREVIOUS ONE...EXCEPT TO BE A LITTLE FASTER. IT IS AGAIN IMPORTANT TO EMPHASIZE THAT...WITH RELIABLE MODELS ON BOTH SIDES OF THE OFFICIAL TRACK...ONE SHOULD NOT FOCUS ON THE EXACT LANDFALL LOCATION IMPLIED BY THE OFFICIAL TRACK. WARNINGS WILL LIKELY BE REQUIRED FOR PORTIONS OF THE HURRICANE AND TROPICAL STORM WATCH AREAS LATER TONIGHT. FORECAST POSITIONS AND MAX WINDS INITIAL 21/2100Z 23.1N 91.2W 45 KT 12HR VT 22/0600Z 24.0N 93.0W 55 KT 24HR VT 22/1800Z 24.9N 94.9W 60 KT 36HR VT 23/0600Z 25.8N 96.1W 70 KT 48HR VT 23/1800Z 26.4N 97.3W 75 KT 72HR VT 24/1800Z 27.0N 99.5W 40 KT...INLAND 96HR VT 25/1800Z...DISSIPATED $$ FORECASTER KNABB |
