ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM HELENE SPECIAL DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072012 430 PM CDT FRI AUG 17 2012 THE AIR FORCE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE REMNANTS OF TROPICAL DEPRESSION SEVEN FOUND A WELL-DEFINED CIRCULATION AND PEAK FLIGHT LEVEL WINDS OF ABOUT 50 KT AND BIAS-CORRECTED SFMR WINDS OF 38 KT. BASED ON THESE DATA...THE SYSTEM IS NOW UPGRADED TO TROPICAL STORM HELENE WITH AN INTENSITY OF 40 KT...ALTHOUGH THESE WINDS COULD BE ENHANCED SOMEWHAT BY TOPOGRAPHY AND DECAYING CONVECTION NEAR THE CENTER. THE SATELLITE PRESENTATION OF THE CYCLONE IS SOMEWHAT LACKLUSTER...WITH MOST OF THE DEEP CONVECTION DISPLACED WEST OF THE CENTER LOCATION. THAT BEING SAID...THERE IS SOME POTENTIAL FOR SLIGHT INTENSIFICATION BEFORE THE CYCLONE MOVES INLAND WITHIN 24 HOURS. AFTER LANDFALL...STEADY DECAY IS EXPECTED TO REMNANT LOW STATUS BY 48 HOURS WITH DISSIPATION EXPECTED BY 72 HOURS. THE INITIAL MOTION ESTIMATE IS A SOMEWHAT UNCERTAIN 310/06. HELENE IS EXPECTED TO MOVE NORTHWESTWARD AND INLAND OVER THE GULF COAST OF MEXICO IN THE NEXT DAY OR SO AS THE MID-LEVEL RIDGE OVER NORTHERN MEXICO AND THE SOUTHWESTERN U.S. RETREATS NORTHWARD. THE NHC FORECAST IS A LITTLE TO THE LEFT OF THE TVCA CONSENSUS AND TO THE RIGHT OF THE ECMWF THROUGH DISSIPATION. THE MAIN THREAT FROM HELENE WILL BE HEAVY RAINFALL...WHICH WILL CONTINUE EVEN AS THE CYCLONE MOVES INLAND AND WEAKENS. FORECAST POSITIONS AND MAX WINDS INIT 17/2130Z 20.6N 96.1W 40 KT 45 MPH 12H 18/0600Z 21.1N 96.9W 45 KT 50 MPH 24H 18/1800Z 22.1N 98.1W 35 KT 40 MPH...INLAND 36H 19/0600Z 22.9N 99.0W 30 KT 35 MPH...INLAND 48H 19/1800Z 23.5N 99.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 20/1800Z...DISSIPATED $$ FORECASTER BRENNAN NNNN
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Page last modified: Monday, 31-Dec-2012 12:09:20 UTC