[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 242100
TCDAT2
TROPICAL STORM KATRINA DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT WED AUG 24 2005

SATELLITE IMAGERY...DOPPLER RADAR DATA FROM THE BAHAMAS AND MIAMI...
AND THE LATEST RECONNAISSANCE WIND DATA INDICATE KATRINA HAS
CONTINUED TO BECOME BETTER ORGANIZED THIS AFTERNOON. BANDING
FEATURES HAVE INCREASED IN ALL QUADRANTS AND THE UPPER-LEVEL
OUTFLOW HAS EXPANDED AND REMAINS QUITE SYMMETRICAL. THE INITIAL
INTENSITY OF 40 KT IS A BLEND OF RECON WIND...38 KT FLIGHT-LEVEL
WINDS...AND PRESSURE DATA...1002 MB OR ROUGHLY 43 KT...AND
SATELLITE INTENSITY ESTIMATES OF 45 KT FROM TAFB AND AFWA. THE
INITIAL POSITION ESTIMATE IS A LITTLE TO SOUTHWEST OF THE 1949Z
RECON POSITION AND IS CLOSE TO THE CENTER OF THE LARGER-SCALE
CIRCULATION BASED ON EXTRAPOLATION OF THE ZERO-ISODOP PATTERN NOTED
IN THE NOAA/NWS MIAMI DOPPLER VELOCITY DATA.

THE INITIAL MOTION ESTIMATE IS 325/08. THERE IS SOME UNCERTAINTY IN
BOTH THE INITIAL MOTION AND THE CENTER POSITION. I HAVE TRIED TO
BLEND THE POSITIONS FROM RECON...RADAR AND SATELLITE DATA. THE LAST
RECON POSITION CAN BE SEEN AS A TIGHT LOW-LEVEL VORTEX MOVING OUT
FROM UNDERNEATH THE DEEP CONVECTION IN THE EAST SEMICIRCLE. IT IS
POSSIBLE THAT THAT VORTEX MAY END UP BEING A TRANSIENT FEATURE. IF
IT TURNS OUT THAT THE CENTER DOES END UP FARTHER NORTH...THEN THE
FORECAST TRACK WILL HAVE TO BE SHIFTED SLIGHTLY NORTHWARD ON THE
NEXT ADVISORY. OTHER THAN THE UNCERTAINTY IN THE INITIAL POSITION
...THE REST OF THE FORECAST TRACK AND REASONING REMAINS UNCHANGED
FROM PREVIOUS ADVISORIES. ALL OF THE NHC MODEL GUIDANCE AGREE ON
THE SUBTROPICAL RIDGE TO THE NORTH OF KATRINA TO KEEP BUILDING
SLOWLY EASTWARD...WHICH ULTIMATELY FORCES THE CYCLONE WESTWARD
ACROSS SOUTH FLORIDA IN 36-48 HOURS...AND INTO THE EASTERN GULF OF
MEXICO BY 72 HOURS. AFTER THAT...HOWEVER...THE MODELS DIFFER
SIGNIFICANTLY ON WHERE AND WHEN KATRINA IS EXPECTED TO TURN
NORTHWARD AND MAKE A SECOND LANDFALL ALONG THE NORTHEAST GULF
COAST. THE GFDN IS THE WESTERNMOST MODEL AND TAKES THE CYCLONE TO
NEW ORLEANS...WHEREAS THE GFS AND CANADIAN MODELS ARE THE
EASTERNMOST MODELS AND TAKE KATRINA NORTHEASTWARD ACROSS THE
NORTHERN FLORIDA PENINSULA. THE OFFICIAL TRACK IS NEAR THE MIDDLE
OF THE GUIDANCE ENVELOPE AND CLOSE TO THE MODEL CONSENSUS.

WITH THE IMPROVED BANDING FEATURES...SYMMETRICAL UPPER-LEVEL OUTFLOW
...AND RELATIVELY WEAK SHEAR...AT LEAST STEADY INTENSIFICATION OF A
NORMAL RATE OF 10 KT PER 12 HOURS UNTIL LANDFALL OCCURS SEEMS
JUSTIFIED. THIS IS SIMILAR TO THE SHIPS INTENSITY MODEL...BUT MUCH
LESS THAN THE NOW VERY BULLISH GFDL MODEL WHICH BRINGS KATRINA TO
111 KT JUST BEFORE LANDFALL. IT SHOULD BE POINTED OUT THAT WITH
SSTS NEAR 31C AND A LOW SHEAR ENVIRONMENT...CONDITIONS ARE
FAVORABLE FOR POSSIBLE RAPID INTENSIFICATION TO OCCUR BETWEEN NOW
AND LANDFALL. THIS IS SUGGESTED BY THE SHIPS MODEL EXPERIMENTAL
RAPID INTENSIFICATION OUTPUT...WHICH INDICATES A 57 PERCENT
PROBABILITY OF THAT OCCURRING. THE ONLY INHIBITING FACTOR IS THE
DRY AIR THAT SURROUNDS KATRINA AND HAS BEEN WORKING ITS WAY INTO
THE INNER-CORE REGION AND ERODING THE DEEP CONVECTION. IF THE DRY
AIR MIXES OUT WITHIN THE NEXT 12 HOURS...THEN INTENSITIES WOULD
LIKELY BE HIGHER THAN THE OFFICIAL FORECAST IS INDICATING.

OWING TO THE SLOW FORWARD SPEED...KATRINA HAS THE POTENTIAL TO
PRODUCE A SIGNIFICANT HEAVY RAINFALL AND FLOODING EVENT ACROSS THE
CENTRAL AND NORTHWEST BAHAMAS...AND EVENTUALLY ACROSS SOUTH
FLORIDA.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      24/2100Z 25.6N  77.2W    40 KT
 12HR VT     25/0600Z 25.9N  77.8W    50 KT
 24HR VT     25/1800Z 26.1N  78.8W    60 KT
 36HR VT     26/0600Z 26.2N  79.7W    70 KT
 48HR VT     26/1800Z 26.3N  80.7W    50 KT...INLAND
 72HR VT     27/1800Z 26.4N  83.0W    55 KT
 96HR VT     28/1800Z 28.0N  85.0W    70 KT
120HR VT     29/1800Z 30.5N  85.0W    65 KT...INLAND


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