ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM TROPICAL STORM LISA SPECIAL DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 AM EDT MON SEP 20 2004 VARIOUS SATELLITE SOURCES AND INTENSITY ESTIMATES INDICATE THAT TROPICAL DEPRESSION THIRTEEN HAS BECOME BETTER ORGANIZED AND HAS STRENGTHENED. THE FIRST FEW VISIBLE SATELITE IMAGES INDICATE A BANDING EYE FEATURE IS TRYING TO DEVELOP...AND A 20/0955Z SSMI OVERPASS REVEALED A SMALL MID-LEVEL EYE WAS PRESENT. SUCH FEATURES ARE TYPICALLY CHARACTERISTIC OF 45-55 KT TROPICAL CYCLONES. THE INITIAL INTENSITY ESTIMATE OF 45 KT IS ALSO SUPPORTED BY A 20/0902Z UW-CIMSS AMSU PRESSURE ESTIMATE OF 999.1 MB. THEREFORE...THE DEPRESSION IS BEING UPGRADED TO TROPICAL STORM LISA. THE INITIAL MOTION ESTIMATE IS 275/10. THERE IS NO CHANGE TO THE PREVIOUS TRACK FORECAST OR REASONING. THIS SPECIAL ADVISORY IS ONLY TO INDICATE THE INCREASE TO TROPICAL STRENGTH...AND AN INCREASE IN THE INTENSITY FORECAST. LISA IS A SMALL AND RATHER COMPACT TROPICAL CYCLONE. AS SUCH...IT IS SUSCEPTIBLE TO SHARP CHANGES IN INTENSITY...BOTH STRENGTHENING AND WEAKENING. THE VERTICAL SHEAR IS FORECAST TO REMAIN AROUND 10 KT OR LESS FOR THE NEXT 24 HOURS...SO STRENGTHENING TO HURRICANE INTENSITY IS FORECAST. AFTER THAT...LOW TO MODERATE VERTICAL SHEAR IS EXPECTED TO POSSIBLY PUT A CAP ON THE INTENSIFICATION TREND...SO ONLY SLOW STRENGTHENING IS FORECAST IN THE 24-48 HOUR PERIOD...WITH A LEVELING OFF OF THE INTENSITY AFTER THAT. HOWEVER...IF LISA TAKES A MORE SOUTHERLY TRACK TO THE LEFT OF THE OFFICIAL FORECAST TRACK ...THEN THE SHEAR WILL BE LESS AND MORE STRENGTHENING WOULD BE POSSIBLE THAN WHAT THE OFFICIAL INTENSITY FORECAST IS INDICATING. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 20/1200Z 13.5N 35.4W 45 KT 12HR VT 20/1800Z 13.6N 36.4W 55 KT 24HR VT 21/0600Z 14.1N 38.2W 65 KT 36HR VT 21/1800Z 14.5N 39.7W 70 KT 48HR VT 22/0600Z 15.0N 41.5W 75 KT 72HR VT 23/0600Z 17.0N 45.0W 75 KT 96HR VT 24/0600Z 18.0N 48.0W 75 KT 120HR VT 25/0600Z 18.5N 51.0W 75 KT $$ NNNN
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Page last modified: Monday, 20-Sep-2004 12:03:23 UTC