[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 272033
TCDAT2
HURRICANE KATRINA DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SAT AUG 27 2005

REPORTS FROM AIR FORCE RESERVE AND NOAA HURRICANE HUNTER AIRCRAFT...
AS WELL AS THE KEY WEST WSR-88D...SHOW THAT KATRINA IS STILL IN A
CONCENTRIC EYEWALL CYCLE WITH THE INNER EYEWALL 9 N MI WIDE AND THE
OUTER 45-50 N MI WIDE.  THE CENTRAL PRESSURE HAS RISEN AS HIGH AS
950 MB...WITH THE LATEST CENTRAL PRESSURE AT 945 MB.  THE AIRCRAFT
HAVE FOUND FLIGHT-LEVEL WINDS AS HIGH AS 119 KT AT 8000 FT IN THE
OUTER EYEWALL...ALTHOUGH MEASUREMENTS FROM THE NOAA STEPPED
FREQUENCY MICROWAVE RADIOMETER SUGGEST THE SURFACE WINDS IN THIS
AREA ARE STILL LESS THAN 100 KT.  THE INITIAL INTENSITY REMAINS
AT 100 KT FOR THIS ADVISORY.

THE INITIAL MOTION REMAINS 275/6.  KATRINA IS SOUTH OF A DEEP-LAYER
RIDGE OVER THE NORTHERN GULF COAST.  THIS RIDGE IS FORECAST TO
WEAKEN AS A STRONG DEEP-LAYER TROUGH DEVELOPS OVER THE CENTRAL
UNITED STATES...AND A NEW DEEP-LAYER RIDGE FORMS OVER THE FLORIDA
PENINSULA AND THE ADJACENT ATLANTIC.  THIS PATTERN CHANGE SHOULD
CAUSE KATRINA TO TURN NORTHWARD DURING THE NEXT 72 HR AND MAKE
LANDFALL OVER THE NORTHERN GULF COAST.  TRACK GUIDANCE REMAINS IN
AGREEMENT WITH THIS SCENARIO...ALTHOUGH THE GFS AND GFDL HAVE LED
AN OVERALL SHIFT TO THE WEST TOWARD SOUTHEAST LOUISIANA.  THIS
SHIFT IS NOT UNANIMOUS...HOWEVER...AS THE UKMET HAS SHIFTED TO THE
EAST OF ITS PREVIOUS TRACK.  THE NEW TRACK IS NUDGED JUST A LITTLE
TO THE WEST OF THE PREVIOUS TRACK...ALONG THE WEST EDGE OF THE MAIN
CLUSTER OF GUIDANCE FOR THE FIRS 24-36 HR AND DOWN THE MIDDLE OF
THAT CLUSTER THEREAFTER.  THE TRACK CALLS FOR LANDFALL IN SOUTHEAST
LOUISIANA IN A LITTLE UNDER 48 HR.

KATRINA SHOULD STRENGTHEN AS IT COMES OUT OF THE CONCENTRIC EYEWALL
CYCLE.  THE GFDL IS NOW CALLING FOR A PEAK INTENSITY OF 131 KT...
WHILE THE SHIPS MODEL IS CALLING FOR 130 KT AND THE FSU
SUPERENSEMBLE 128 KT.  THE INTENSITY FORECAST WILL CALL FOR
STRENGTHENING TO 125 KT AT LANDFALL...AND THERE REMAINS A CHANCE
THAT KATRINA COULD BECOME A CATEGORY FIVE HURRICANE BEFORE
LANDFALL.  THERE REMAINS THE POSSIBILITY OF ANOTHER CONCENTRIC
EYEWALL CYCLE BEFORE LANDFALL...WHICH COULD THROW OFF THE INTENSITY
FORECAST A BIT.

THE NEW FORECAST TRACK AND WIND RADII REQUIRE A HURRICANE WATCH FOR
AND EXPANDED PORTIONS OF THE NORTHERN GULF COAST AT THIS TIME.
HURRICANE WARNINGS WILL LIKELY BE REQUIRED LATER TONIGHT FOR PARTS
OF THE WATCH AREA.

FORECASTER BEVEN


FORECAST POSITIONS AND MAX WINDS

INITIAL      27/2100Z 24.6N  85.6W   100 KT
 12HR VT     28/0600Z 24.9N  86.8W   105 KT
 24HR VT     28/1800Z 25.8N  88.3W   115 KT
 36HR VT     29/0600Z 27.5N  89.6W   120 KT
 48HR VT     29/1800Z 29.6N  90.0W   125 KT
 72HR VT     30/1800Z 34.0N  89.0W    60 KT...INLAND
 96HR VT     31/1800Z 38.5N  85.0W    30 KT...INLAND
120HR VT     01/1800Z 43.0N  78.5W    25 KT...EXTRATROPICAL


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