[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 252108
TCDAT2
HURRICANE KATRINA DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT THU AUG 25 2005

KATRINA IS NOW A HURRICANE BASED ON NOAA RECON SFMR REPORTS OF
SURFACE WINDS TO 64 KT JUST NORTHWEST OF THE CENTER. THESE WINDS
ARE SUPPORTED BY NOAA-MIAMI DOPPLER RADAR VELOCITIES OF 90 KT AT
3000 FT...WHICH EQUATES TO ABOUT 67 KT SURFACE WINDS. THE MOST
RECENT NOAA RECON PRESSURE WHILE COMPOSING THIS DISCUSSION HAS
FALLEN 2 MB IN THE PAST HOUR TO 985 MB.

THE INITIAL MOTION ESTIMATE IS 265/5. 12Z AND 18Z UPPER-AIR DATA
INDICATE THE SUBTROPICAL RIDGE TO THE NORTH OF KATRINA HAS CHANGED
LITTLE WHILE AN INVERTED MID- TO UPPER-LEVEL TROUGH HAS DEVELOPED
NORTHWARD FROM THE CARIBBEAN SEA TO KATRINA. THE TROUGH IS EXPECTED
TO INDUCE A SLIGHT SOUTH OF DUE WEST MOTION FOR THE NEXT 12 HOURS
OR SO. AFTERWARDS...THE RIDGE TO THE NORTH IS EXPECTED TO SLOWLY
WEAKEN AND ERODE ON THE WEST SIDE AS A SHORTWAVE TROUGH OVER THE
CENTRAL U.S. DIGS SOUTHEASTWARD TOWARD THE NORTHERN GULF OF MEXICO.
THIS SLOW EVOLVING PATTERN IS FOECAST TO GRADUALLY INDUCE A SLOW
NORTHWEST AND THEN NORTHWARD MOTION AFTER 48 HOURS. THE NHC MODEL
GUIDANCE IS IN GOOD AGREEMENT ON THE WESTWARD MOTION FOR THE NEXT
36 HOURS...BUT THEN DIVERGES SIGNIFICANTLY AFTER THAT. THE GFS HAS
BEEN THE MOST CONSISTENT/PERSISTENT MODEL IN TAKING KATRINA SLOWLY
NORTHEASTWARD AFTER 72 HOURS ACROSS NORTHWEST FLORIDA...WHEREAS THE
GFDL...GFDN...AND UKMET MODELS HAVE NOW FLIP-FLOPPED WIDELY TO THE
WEST AND BRING KATRINA INLAND BETWEEN MOBILE ALABAMA AND GRAND ISLE
LOUISIANA. THE GFDL AND GFDN MODELS HAVE BEEN GIVEN LESS WEIGHT
GIVEN THEIR PERSISTENT MUCH FASTER WESTWARD MOTION THE PAST 24
HOURS...WHICH HAS NOT MATERIALIZED. THE OFFICIAL FORECAST TRACK IS
SIMILAR TO THE PREVIOUS TRACK AND IS TO THE RIGHT OF THE NHC MODEL
CONSENSUS.

THERE IS STILL A SHORT WINDOW OF OPPORTUNITY FOR KATRINA TO
STRENGTHEN TO AROUND 70 KT BEFORE LANDFALL OCCURS. AFTER LANDFALL
...STEADY WEAKENING IS EXPECTED UNTIL THE HURRICANE EMERGES OFF THE
SOUTHWEST FLORIDA COAST IN ABOUT 30 HOURS. ONCE KATRINA MOVES OVER
THE WARM GULF OF MEXICO WHERE THE VERTICAL SHEAR IS EXPECTED TO BE
LOW...RESTRENGTHENING INTO A HURRICANE SEEMS LIKELY. IT SHOULD BE
EMPHASIZED THAT KATRINA IS NOT FORECAST TO WEAKEN PRIOR TO LANDFALL
...WHICH COULD BE IMPLIED BY THE OFFICIAL INTENSITY FORECAST. IN
CONTRAST...KATRINA IS EXPECTED TO STRENGTHEN TO 90 KT BEFORE
LANDFALL OCCURS IN THE FLORIDA PANHANDLE. THIS IS CONSISTENT WITH
THE SHIPS INTENSITY MODEL AND THE TREND IN THE GFDL MODEL...
ALTHOUGH THE LATTER MODEL MAKES KATRINA A 118-KT CATEGORY 4 STORM.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      25/2100Z 26.1N  79.9W    65 KT
 12HR VT     26/0600Z 26.1N  80.7W    45 KT...INLAND
 24HR VT     26/1800Z 26.1N  81.7W    40 KT...INLAND
 36HR VT     27/0600Z 26.4N  82.8W    50 KT...OVER WATER
 48HR VT     27/1800Z 27.0N  83.7W    60 KT
 72HR VT     28/1800Z 28.5N  85.0W    80 KT
 96HR VT     29/1800Z 31.5N  84.5W    40 KT...INLAND
120HR VT     30/1800Z 35.0N  81.5W    25 KT...INLAND

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