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| #34582 (Received by flhurricane at: 11:11 PM 21.Jul.2005) TCDAT1 TROPICAL STORM FRANKLIN DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT THU JUL 21 2005 THE LAST REPORTS FROM THE RECONNAISSANCE AIRCRAFT SHORTLY BEFORE 00Z INDICATED THAT THE CENTRAL PRESSURE REMAINED 1009 MB... AND MAXIMUM 1000 FT FLIGHT LEVEL WINDS AS STRONG AS 57 KT WERE MEASURED WITHIN A CONVECTIVE BURST RIGHT NEAR THE CIRCULATION CENTER. THIS WOULD NORMALLY CORRESPOND TO SURFACE WINDS OF ABOUT 45 KT... BUT SINCE THE PRESSURE WAS RELATIVELY HIGH AND THE CONVECTIVE PATTERN REMAINS QUITE DISORGANIZED... WITH DVORAK T NUMBERS AT 2.0 AND 2.5... THE INITIAL INTENSITY IS HELD AT 40 KT. RECON WILL ONCE AGAIN INVESTIGATE FRANKLIN ON FRIDAY MORNING. THE INITIAL MOTION IS 310/11. FRANKLIN IS MOVING TOWARD THE NORTHWEST WITHIN A RELATIVE WEAKNESS IN THE SUBTROPICAL RIDGE. IT IS EXPECTED TO SLOW DOWN DURING THE NEXT COUPLE OF DAYS... AND BE WITHIN AN AREA OF WEAK STEERING CURRENTS TO THE SOUTH OF A MIDLATITUDE TROUGH AND TO THE SOUTHEAST OF A BUILDING MID-LEVEL RIDGE OVER THE SOUTHEASTERN UNITED STATES. MOST OF THE DYNAMICAL MODELS FORECAST THE MIDLATITUDE TROUGH TO PROVIDE ENOUGH IMPETUS TOWARD THE EAST TO RECURVE FRANKLIN TOWARD THE OPEN ATLANTIC. HOWEVER... AN ALTERNATIVE SCENARIO IS THAT THE TROUGH WILL BYPASS FRANKLIN AND ALLOW THE SOUTHEASTERN U.S. RIDGE TO HALT ITS EXODUS OUT TO SEA AND PERHAPS EVEN EVENTUALLY STEER IT BACK TO THE WEST. THE OFFICIAL FORECAST IS A COMPROMISE BETWEEN THESE SCENARIOS AND IS A LITTLE FASTER TO THE NORTHEAST THAN THE PREVIOUS FORECAST. FRANKLIN IS LOCATED BETWEEN AN UPPER-LEVEL RIDGE AND AN UPPER-LEVEL SHEAR AXIS WHICH IS IMPARTING SOME WESTERLY SHEAR. HOWEVER... THE SHEAR AXIS IS EXPECTED TO WEAKEN... WHICH COULD ALLOW FRANKLIN TO GRADUALLY INTENSIFY DURING THE NEXT COUPLE OF DAYS. ALONG THE OFFICIAL FORECAST TRACK... THE TROPICAL STORM WOULD REMAIN OVER 27-28C SSTS EVEN LATE IN THE FORECAST PERIOD AND PERHAPS BE IMPACTED BY MODERATE NORTHERLY SHEAR. INTENSIFICATION TO A HURRICANE IS HIGHLY UNCERTAIN. IF FRANKLIN MOVES MORE QUICKLY OUT TO SEA... THIS WOULD BE UNLIKELY... BUT IF IT BECOMES TRAPPED SOUTH OF THE SUBTROPICAL RIDGE LATE IN THE FORECAST PERIOD... THE ENVIRONMENT COULD BECOME FAVORABLE FOR MORE INTENSIFICATION THAN IS CURRENTLY FORECAST. FRANKLIN IS THE EARLIEST SIXTH TROPICAL STORM ON RECORD IN THE ATLANTIC BASIN. FORECASTER KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 22/0300Z 26.1N 76.3W 40 KT 12HR VT 22/1200Z 27.2N 77.3W 45 KT 24HR VT 23/0000Z 28.5N 77.4W 50 KT 36HR VT 23/1200Z 29.5N 77.1W 55 KT 48HR VT 24/0000Z 30.0N 76.5W 55 KT 72HR VT 25/0000Z 30.5N 75.5W 60 KT 96HR VT 26/0000Z 31.0N 74.5W 60 KT 120HR VT 27/0000Z 31.0N 73.5W 60 KT |
