[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 251504
TCDAT2
TROPICAL STORM KATRINA DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT THU AUG 25 2005

KATRINA HAS BECOME BETTER ORGANIZED BASED ON DOPPLER RADAR DATA AND
SATELLITE IMAGERY. A FEW ISOLATED DOPPLER VELOCITIES AS HIGH AS 68
KT AT 9000-10000 FT HAVE OCCASIONALLY BEEN OBSERVED...BUT THE
AVERAGE DOPPLER VELOCITIES OVER A 1-NMI STRETCH HAVE BEEN AROUND 55
KT...WHICH EQUATES TO ROUGHLY 50-KT SURFACE WINDS. THIS IS
CONSISTENT WITH A BLEND OF SATELLITE INTENSITY ESTIMATES OF 45 KT
FROM TAFB AND AFWA...AND 55 KT FROM SAB. A NOAA P-3 RECONNAISSANCE
AIRCRAFT WITH SFMR CAPABILITY IS CURRENTLY INVESTIGATING KATRINA...
AND A RECENT REPORT INDICATES THE PRESSURE IS NOW LOWER AT 990 MB.
HOWEVER... THIS PRESSURE DROP HAS NOT YET TRANSLATED INTO A
CORRESPONDING INCREASE IN WINDS.

THE INITIAL MOTION ESTIMATE IS 270/5. 06Z AND 12Z UPPER-AIR DATA
INDICATE THE SUBTROPICAL RIDGE TO THE NORTH OF KATRINA HAS
CONTINUED TO SHIFT SLOWLY EASTWARD ALONG 32N LATITUDE. THIS HAS
CREATED A DEEP-LAYER EASTERLY STEERING CURRENT...ALBEIT A WEAK ONE.
THE NHC MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON KATRINA
MOVING GENERALLY WESTWARD ACROSS THE SOUTHERN FLORIDA PENINSULA FOR
THE NEXT 48 HOURS OR SO. AFTER THAT...HOWEVER...THE MODELS CONTINUE
TO DIVERGE SIGNIFICANTLY ON WHEN AND WHERE THE TURN TO THE NORTH
TOWARD THE FLORIDA PANHANDLE OR NORTHWEST FLORIDA IS EXPECTED TO
OCCUR. THE UKMET IS THE EASTERNMOST AND FASTEST MODEL AND BRINGS
KATRINA ACROSS NORTHEAST FLORIDA...WHEREAS THE GFDL IS THE
WESTERNMOST MODEL AND TAKES THE CYCLONE ACROSS THE WESTERN FLORIDA
PANHANDLE. THE REST OF THE MODELS ARE EVENLY DISTRIBUTED BETWEEN
THESE SOLUTIONS. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE
PREVIOUS TRACK AND IS CLOSE TO THE NHC MODEL CONSENSUS AFTER 48
HOURS. THE GFDL MODEL HAS BEEN CONSISTENTLY FORECASTING A
SOUTHWESTWARD MOTION AROUND THE SOUTHERN END OF FLORIDA FOR THE
PAST 24 HOURS. WHILE THIS TRACK IS CERTAINLY POSSIBLE TO SOME
DEGREE...MY CURRENT THINKING IS THAT THE GFDL IS TAKING KATRINA TOO
FAR SOUTH THROUGH THE FLORIDA KEYS AS A MAJOR HURRICANE.

THE AFOREMENTIONED UPPER-AIR DATA INDICATE MID-LEVEL DRY AIR HAS
GRADUALLY BEEN MOVING SOUTHWARD ACROSS THE FLORIDA PENINSULA AND
KATRINA HAS BEEN MOVING ALONG THE NORTHERN EDGE OF A SHARP MOISTURE
GRADIENT. THIS HAS RESULTED IN OCCASIONAL INTRUSIONS OF DRY AIR
INTO THE INNER CORE AND HAS CAUSED THE CONVECTION TO WEAKEN.
HOWEVER...OVER THE PAST FEW HOURS...RADAR DATA FROM MELBOURNE AND
MIAMI INDICATE NUMEROUS SMALL BANDS OF CONVECTION ARE DEVELOPING IN
THE LARGE DRY SLOT TO THE NORTH...AND A BANDING EYE FEATURE HAS
BEEN TRYING TO DEVELOP. GIVEN THE SLOW FORWARD SPEED OVER THE VERY
WARM GULFSTREAM AND THE FAVORABLE OUTFLOW PATTERN...KATRINA COULD
STILL POSSIBLY REACH CATEGORY ONE HURRICANE STRENGTH PRIOR TO
LANDFALL. KATRINA WILL WEAKEN AS IT MOVES OVER SOUTH FLORIDA...AND
THEN RE-STRENGTHENING IS EXPECTED ONCE IT MOVES OVER THE WARM GULF
OF MEXICO WHERE THE VERTICAL SHEAR IS FORECAST TO BE QUITE LOW. IT
SHOULD BE NOTED THAT KATRINA IS NOT EXPECTED TO WEAKEN PRIOR TO
LANDFALL...WHICH COULD BE IMPLIED BY THE OFFICIAL INTENSITY
FORECAST. IN FACT...KATRINA WILL PROBABLY CONTINUE TO STRENGTHEN
RIGHT UP UNTIL LANDFALL OCCURS IN THE FLORIDA PANHANDLE.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      25/1500Z 26.2N  79.3W    50 KT
 12HR VT     26/0000Z 26.2N  80.0W    65 KT
 24HR VT     26/1200Z 26.2N  81.0W    45 KT...INLAND
 36HR VT     27/0000Z 26.3N  82.0W    40 KT
 48HR VT     27/1200Z 26.7N  83.0W    50 KT
 72HR VT     28/1200Z 28.1N  84.3W    70 KT
 96HR VT     29/1200Z 30.5N  84.5W    60 KT...INLAND
120HR VT     30/1200Z 34.0N  82.0W    25 KT...DISSIPATING INLAND

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