[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 100300
TCDAT1
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

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