[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 290249
TCDAT2
HURRICANE KATRINA DISCUSSION NUMBER  25
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN AUG 28 2005

THERE ARE CONFLICTING SIGNALS REGARDING THE INTENSITY OF KATRINA.
THE NOAA AIRCRAFT NEAR 00Z REPORTED A PEAK FLIGHT LEVEL WIND OF 155
KT...WHICH WOULD NORMALLY CORRESPOND TO 140 KT AT THE SURFACE.  THE
PRESSURE REMAINS EXTREMELY LOW...904 MB AT LAST REPORT.  ON THE
OTHER HAND...THE STEPPED-FREQUENCY MICROWAVE RADIOMETER...OR
SFMR...SUGGESTED WINDS WERE IN THE 120-130 KT RANGE...AND LIMITED
DROPSONDE DATA ALSO SUGGESTED SOMETHING A LITTLE BELOW 140 KT.
THERE ARE ENOUGH QUESTIONS ABOUT THE PERFORMANCE OF THE SFMR AT
THESE SPEEDS FOR ME TO STICK WITH THE STANDARD 90 PERCENT
ADJUSTMENT FOR NOW.

THERE HAVE BEEN SOME MODEST CHANGES IN THE STRUCTURE OF KATRINA OVER
THE LAST SEVERAL HOURS. RECENT MICROWAVE PASSES SHOW THAT AN OUTER
EYEWALL IS IN THE FORMATIVE STAGES...AND THE LATEST IR IMAGES SHOW
A LESS WELL-DEFINED EYEWALL WITH MORE EVIDENCE OF OUTER BANDING.
THE NOAA HURRICANE HUNTERS ALSO REPORTED AN EROSION OF THE EYEWALL
IN THE SOUTHWEST QUADRANT. THESE OBSERVATIONS SUGGEST THAT THERE
COULD BE SOME WEAKENING OF KATRINA PRIOR TO LANDFALL. ALL THIS IS
RELATIVE...HOWEVER...AND KATRINA IS STILL EXPECTED TO BE OF AT
LEAST CATEGORY FOUR INTENSITY WHEN IT REACHES THE COAST. AN EYEWALL
REPLACEMENT AT THIS POINT IS NOT ALL GOOD NEWS...AS THEY ARE
GENERALLY ACCOMPANIED BY A BROADENING OF THE WIND FIELD...SO THAT
EVEN AS KATRINA WEAKENS THERE COULD BE AN INCREASE IN THE AREA THAT
EXPERIENCES MAJOR HURRICANE FORCE WINDS.

THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE TRACK FORECAST.  THE
INITIAL MOTION IS 335/9.  KATRINA IS EXPECTED TO GRADUALLY TURN
NORTHWARD INTO A BREAK IN THE SUBTROPICAL RIDGE ASSOCIATED WITH A
LARGE MID-LATITUDE CYCLONE NEAR THE GREAT LAKES.  MODEL GUIDANCE
REMAINS TIGHTLY CLUSTERED...WITH THE NOGAPS SHIFTING JUST A BIT
EAST OF ITS PREVIOUS TRACK.  WHILE THERE IS GREAT SIGNIFICANCE FOR
THE CITY OF NEW ORLEANS IN THE DETAILS OF THE TRACK...TRACK
ANOMOLIES OF 30-50 MILES ARE STILL POSSIBLE EVEN 12-18 HOURS OUT.

FORECASTER FRANKLIN


FORECAST POSITIONS AND MAX WINDS

INITIAL      29/0300Z 27.6N  89.4W   140 KT
 12HR VT     29/1200Z 29.2N  89.7W   135 KT
 24HR VT     30/0000Z 31.8N  89.5W    85 KT...INLAND
 36HR VT     30/1200Z 34.8N  88.1W    45 KT...INLAND
 48HR VT     31/0000Z 37.7N  85.9W    30 KT...INLAND
 72HR VT     01/0000Z 43.5N  78.5W    25 KT...INLAND
 96HR VT     02/0000Z 50.0N  70.0W    25 KT...EXTRATROPICAL
120HR VT     03/0000Z...ABSORBED


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