[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 261506
TCDAT2
HURRICANE KATRINA DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT FRI AUG 26 2005

RECENT DATA FROM AN AIR FORCE RECON AIRCRAFT INDICATES KATRINA'S
CENTRAL PRESSURE IS MUCH LOWER...NOW AT 971 MB. MAXIMUM 700 MB
FLIGHT-LEVEL WINDS ARE 81 KT IN THE NORTHWEST QUADRANT...WHICH
SUPPORTS AT LEAST 70 KT SURFACE WINDS. HOWEVER...THE AIRCRAFT HAS
NOT SAMPLED THE WINDS IN THE EASTERN SEMICIRCLE WHERE NOAA/KEY WEST
DOPPLER RADAR VELOCITY DATA INDICATES WINDS AS HIGH AS 91 KT AT
AROUND 3000 FT...WHICH WOULD SUPPORT A SURFACE WIND ESTIMATE OF
ABOUT 75 KT. THE INITIAL INTENSITY OF 70 KT MAY TURN OUT TO BE A
LITTLE LOW.

THE INITIAL MOTION ESTIMATE IS 265/6. RADAR DATA INDICATES KATRINA
HAS CONTINUED TO MOVE SOUTH OF DUE WEST DURING THE PAST 6 HOURS.
MOST OF THE NHC MODEL GUIDANCE INDICATES THE TRACK SHOULD FLATTEN
OUT IN A MORE WESTWARD DIRECTION DURING THE NEXT 12 HOURS AS THE
INFLUENCE OF AN INVERTED TROUGH OVER THE CARIBBEAN SEA DECREASES.
THE MID-LEVEL SUBTROPICAL RIDGE TO THE NORTH AND NORTHWEST OF
KATRINA IS FORECAST BY THE ALL GLOBAL AND REGIONAL MODELS TO
GRADUALLY WEAKEN THROUGH THE FORECAST PERIOD AS A STRONG SHORTWAVE
TROUGH OVER THE CENTRAL U.S. DIGS SOUTHEASTWARD TOWARD THE NORTHERN
GULF OF MEXICO AND SOUTHEASTERN UNITED STATES. THE TIMING OF THE
EROSION OF THE RIDGE AND AN INDUCED NORTHWARD MOTION OF KATRINA IS
THE MAIN DIFFERENCE BETWEEN THE MODELS...WHICH HAS RESULTED IN A
LARGE SPREAD AFTER 48 HOURS. THE NOGAPS AND GFDN MODELS HAVE MADE A
LARGE JUMP TO THE WEST OVER LOUISIANA...WHEREAS THE MAJORITY OF THE
NHC MODELS TAKE KATRINA INLAND OVER THE NORTHEAST GULF COAST. THE
OFFICIAL FORECAST TRACK REMAINS IN THE RIGHT PORTION OF THE MODEL
GUIDANCE ENVELOPE.

STRENGTHENING TO A MAJOR HURRICANE IS EXPECTED. IN FACT...A RECENT
DROPSONDE REPORT RECEIVED FROM THE RECONNAISSANCE AIRCRAFT
INDICATES MAXIMUM WINDS ARE NOW UP TO 80 KT. SO...A SPECIAL
ADVISORY WILL BE ISSUED SHORTLY TO UPDATE THE CURRENT AND FORECAST
INTENSITIES.

FORECASTER STEWART


FORECAST POSITIONS AND MAX WINDS

INITIAL      26/1500Z 25.1N  82.2W    70 KT
 12HR VT     27/0000Z 25.2N  83.1W    75 KT
 24HR VT     27/1200Z 25.5N  84.3W    80 KT
 36HR VT     28/0000Z 26.2N  85.2W    85 KT
 48HR VT     28/1200Z 27.1N  85.9W    90 KT
 72HR VT     29/1200Z 29.5N  86.3W   100 KT
 96HR VT     30/1200Z 34.5N  83.5W    35 KT...INLAND
120HR VT     31/1200Z 40.5N  77.0W    25 KT...DISSIPATING INLAND


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