ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IDA DISCUSSION NUMBER 25 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009 900 PM CST MON NOV 09 2009 RADAR AND SATELLITE IMAGES SHOW THE CONVECTION THAT WAS NEAR THE CENTER DURING THE AFTERNOON HAS WEAKENED AND SHEARED OFF TOWARD THE NORTH. THIS WAS CONFIRMED BY A RECENT AIRCRAFT FIX THAT POSITIONED THE CENTER EAST OF SOUTHEASTERN LOUISIANA WELL SOUTH OF THE REMAINING DEEP CONVECTION. THE FORWARD SPEED OF IDA HAS SLOWED TO ABOUT 11 KT. THE DYNAMICAL MODEL GUIDANCE FORECASTS A CONTINUED REDUCTION IN THE FORWARD MOTION OF THE STORM AND A TURN TOWARD THE EAST AFTER LANDFALL. THE NHC FORECAST IS CLOSE TO THE PREVIOUS ADVISORY THROUGH 12 HOURS AND IS THEN ADJUSTED A LITTLE NORTHWARD CLOSER TO THE MODEL CONSENSUS. THE AIRCRAFT HAS RECENTLY MEASURED A PEAK 850 MB FLIGHT-LEVEL WIND OF 71 KT AND A SMFR SURFACE WIND OF 51 KT. THIS SUPPORTS AN INITIAL INTENSITY OF 55 KT. IDA SHOULD GRADUALLY WEAKEN THROUGH LANDFALL DUE TO INCREASING SHEAR AND COOLER SSTS. ONCE INLAND THE CYCLONE WILL WEAKEN AT A FASTER RATE AND BECOME EXTRATROPICAL SHORTLY THEREAFTER. MOST OF THE GLOBAL MODELS SHOW THE CYCLONE BEING ABSORBED BY A FRONTAL BOUNDARY IN 36-48 HOURS AND SO DOES THE OFFICIAL FORECAST. THE LOCATION AND TIMING OF IDA'S LANDFALL WILL HAVE LITTLE SIGNIFICANCE SINCE THE TROPICAL STORM FORCE WINDS COVER A LARGE AREA AND MOST OF THE HEAVIER RAINFALL IS ALREADY SPREADING ONSHORE. FORECAST POSITIONS AND MAX WINDS INITIAL 10/0300Z 29.3N 88.6W 55 KT 12HR VT 10/1200Z 30.8N 87.9W 40 KT...EXTRATROPICAL 24HR VT 11/0000Z 31.5N 86.5W 30 KT...EXTRATROPICAL 36HR VT 11/1200Z 31.3N 84.8W 25 KT...EXTRATROPICAL 48HR VT 12/0000Z...DISSIPATED $$ FORECASTER BROWN/BERG NNNN
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Page last modified: Thursday, 31-Dec-2009 12:09:12 UTC