[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 210830
TCDAT1
HURRICANE JEANNE DISCUSSION NUMBER  31
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT TUE SEP 21 2004

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE
THAT THE CENTRAL PRESSURE OF JEAN HAS FALLEN TO 972 MB...WITH
MAXIMUM FLIGHT-LEVEL WINDS OF 93 KT AT 850 MB IN THE SOUTHWEST
QUADRANT.  THE AIRCRAFT ALSO REPORTED A 45 NM WIDE EYE...OPEN TO
THE SOUTH...WHICH SATELLITE IMAGERY INDICATES IS MOSTLY CLOUDED
OVER.  SATELLITE INTENSITY ESTIMATES ARE 77 KT FROM TAFB AND
SAB...AND 65 KT FROM AFWA.  THE INITIAL INTENSITY IS INCREASED TO
80 KT BASED MAINLY ON THE 11 MB PRESSURE FALL SINCE THE LAST
RECONNAISSANCE MISSION.

THE INITIAL MOTION IS 070/5.  ALL GUIDANCE AGREES THAT JEANNE SHOW
SLOW AND TURN SOUTHEASTWARD DURING THE NEXT 24 HR OR SO AS A HIGH
PRESSURE RIDGE BUILDS TO THE NORTH.  AFTER THAT...MODEL DIVERGENCE
IS AGAIN PRESENT.  THE GFS STILL WANT TO TAKE JEANNE OFF TO THE
EAST.  ON THE OTHER HAND...THE UKMET AND NOGAPS HAVE SHIFTED
CONSIDERABLY TO THE WEST OF THEIR PREVIOUS FORECASTS...CALLING FOR
JEANNE TO LOOP WESTWARD BEFORE TURNING NORTHWESTWARD BY DAY 5.  IT
SHOULD BE NOTED THAT NEITHER OF THESE MODELS INITIALLY MOVE JEANNE
AS FAR EAST AS IT IS NOW.  THE GFDL IS IN BETWEEN THESE EXTREMES...
CALLING FOR A LESS DRASTIC WESTWARD MOTION DURING THE LOOP.  THE
OFFICIAL FORECAST WILL CHANGE PHILOSOPHY TO THAT A LOOP WESTWARD
AND THEN NORTHWESTWARD BY DAY 5...BUT NOT AS FAR WEST AS THE UKMET
AND THE NOGAPS.  THIS LOW CONFIDENCE FORECAST TRACK IS IN BEST
AGREEMENT WITH THE GFDL AND GUNA.

ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATES 20 KT
OF WEST-SOUTHWESTERLY SHEAR ACROSS JEANNE AT THIS TIME.  THIS
SUGGESTS THAT THE OBSERVED DEEPENING SHOULD SOON CEASE IF IT HAS
NOT ALREADY DONE SO.  THE SHIPS MODEL INDICATES THE SHEAR SHOULD
PERSIST FOR 24-36 HR AND THEN GRADUALLY SUBSIDE.  THIS COULD ALLOW
SOME ADDITIONAL STRENGTHENING IF JEANNE DOES NOT SHEAR OFF BEFORE
THEN...INGEST THE AIR BEHIND THE COLD FRONT JUST TO THE NORTH...OR
UPWELL COLD WATER UNDERNEATH IT WHILE MAKING ITS SLOW LOOP.  THE
INTENSITY FORECAST WILL CALL FOR SLIGHT STRENGTHENING AT 48 HR ON
THE ASSUMPTION THAT NONE OF THESE THINGS WILL HAPPEN.  AFTER 72
HR...SHIPS FORECASTS AN INCREASE IN SHEAR.  HOWEVER...LARGE-SCALE
MODELS HAVE A VARIETY OF SOLUTIONS FOR THE UPPER-LEVEL WINDS NEAR
JEANNE AT THAT TIME RANGING FROM FAVORABLE TO UNFAVORABLE...AND IT
IS UNCLEAR AT THIS TIME WHICH MODEL HAS THE BEST GRASP OF THE
EVOLUTION.  THE INTENSITY FORECAST WILL THUS LEAN ON THE SHIPS
MODEL AND CALL FOR WEAKENING AT 96-120 HR.  THE INTENSITY FORECAST
REMAINS LOW CONFIDENCE.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL      21/0900Z 27.6N  70.0W    80 KT
 12HR VT     21/1800Z 27.6N  69.6W    80 KT
 24HR VT     22/0600Z 27.1N  69.3W    80 KT
 36HR VT     22/1800Z 26.5N  69.5W    80 KT
 48HR VT     23/0600Z 26.3N  70.0W    85 KT
 72HR VT     24/0600Z 26.6N  71.0W    85 KT
 96HR VT     25/0600Z 27.5N  72.0W    75 KT
120HR VT     26/0600Z 29.0N  73.0W    65 KT


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