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| #9723 (Received by flhurricane at: 10:50 AM 23.Sep.2004) TCDAT4 TROPICAL STORM IVAN DISCUSSION NUMBER 70 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT THU SEP 23 2004 A BURST OF DEEP CONVECTION FIRED OFF NEAR THE LOW-LEVEL CENTER EARLIER THIS MORNING AND AIR FORCE RESERVE RECON FOUND 70 KT 1500 FT FLIGHT-LEVEL WINDS...OR EQUAL TO ABOUT 56 KT SURFACE WINDS... AND A PRESSURE OF 998 MB. HOWEVER...SINCE THEN THE CONVECTION HAS WEAKENED AND A SUBSEQUENT PASS THROUGH THE CENTER INDICATED A CENTRAL PRESSURE OF 1000 MB. THE INITIAL INTENSITY OF 50 KT IS A BLEND OF A 45 KT SURFACE WIND SUPPORTED BY THE 1000 MB PRESSURE... AND THE 56 KT SURFACE WIND CONVERSION. THE INITIAL MOTION ESTIMATE IS 310/13. IVAN IS EXPECTED TO MOVE NORTHWESTWARD TO WEST-NORTHWESTWARD AND BE INLAND WITHIN THE NEXT 12 HOURS OVER SOUTHWESTERN LOUISIANA OR THE UPPER-TEXAS COAST. AFTERWARDS...RAPID WEAKENING SHOULD ALLOW THE LOW-LEVEL CIRCULATION TO DECOUPLE FROM THE MID- AND UPPER-LEVEL CIRCULATIONS. THIS WILL ALLOW THE LOW-LEVEL CIRCULATION TO BE STEERED SLOWLY WEST AND SOUTHWESTWARD BY A LARGE RIDGE FORECAST TO BUILD EASTWARD OVER THE CENTRAL AND SOUTHERN PLAINS STATES IN 36-48 HOURS. THIS TRACK SCENARIO IS CONSISTENT WITH THE SHALLOW BAM MODEL...AND THE MOST OF THE GLOBAL MODELS. WHILE IVAN IS NOT EXPECTED TO BE A PROLIFIC WIND PRODUCER...ITS SLOW FORWARD SPEED FOR THE NEXT SEVERAL DAYS MAY BRING UP LARGE AMOUNTS OF GULF MOISTURE THAT COULD RESULT IN LOCALLY HEAVY RAINFALL. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 23/1500Z 29.2N 92.7W 50 KT 12HR VT 24/0000Z 30.0N 94.0W 45 KT...INLAND 24HR VT 24/1200Z 30.5N 95.3W 30 KT...INLAND 36HR VT 25/0000Z 30.6N 96.3W 25 KT...INLAND 48HR VT 25/1200Z 30.4N 97.0W 20 KT...DISSIPATING INLAND 72HR VT 26/1200Z 29.5N 97.8W 20 KT...REMNANT LOW INLAND 96HR VT 27/1200Z...DISSIPATED INLAND |
