[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 180251
TCDAT1
TROPICAL STORM JEANNE DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT FRI SEP 17 2004

A USAF RESERVE UNIT AIRCRAFT LOCATED THE CENTER JUST OFFSHORE FROM
HISPANIOLA WITH A 1000 MB CENTRAL PRESSURE AND A MAXIMUM 1500 FOOT
FLIGHT LEVEL WIND OF 55 KT ABOUT 10 NMI NORTH OF THE CENTER.
INFRARED SATELLITE IMAGES SHOW THE VERY SMALL AND EXPOSED LOW LEVEL
CIRCULATION CENTER WITH THE DEEP CONVECTION ON THE EAST SIDE.  THE
WESTERLY SHEAR APPEARS TO BE AROUND 5 TO 10 KTS BASED UPON THE
LATEST UW CIMSS ANALYSIS.  BASED ON THIS...AND SATELLITE INTENSITY
ESTIMATES OF 55 KTS...JEANNE IS UPGRADED BACK TO A TROPICAL STORM
WITH A 40 KT WIND MAXIMUM.  JEANNE IS VERY SMALL AND THE 34 KT
SURFACE WINDS EXTEND OUT ONLY ABOUT 15 NMI FROM THE CENTER IN THE
NORTHERN SEMI-CIRCLE.

THE INITIAL MOTION ESTIMATE IS 315/05...BUT THE SPEED MAY BE
GENEROUS...AS THE LATEST SATELLITE IMAGES SHOW THAT THE SYSTEM MAY
BE SLOWING DOWN AGAIN. THE GUIDANCE IS REASONABLY CLUSTERED OUT TO
ABOUT 48 HOURS...EXCEPT FOR THE GFS WHICH TAKES THE SYSTEM TOWARD
THE NORTHEAST AND THEN...AFTER 3 DAYS...DOES A GRAND LOOP TO THE
RIGHT DOWN TO THE SOUTH. THE GFDL FOLLOWS THE GFS SCENARIO BUT ON A
MORE MODEST SCALE.  ON THE LEFT SIDE WE HAVE THE UKMET AND NOGAPS
GOING OFF TO THE WEST OR SOUTHWEST.  SINCE THERE IS SO MUCH
UNCERTAINTY AT THE LONGER RANGES I HAVE DONE WHAT THE PREVIOUS
FORECASTER DID AND MOVED ALONG GUIDANCE CONSENSUS TO THE 3 DAY
POSITION AND LEFT IT THERE FOR DAY 4 AND 5.  EXACTLY WHAT HAPPENS
IS DEPENDENT ON THE EVOLUTION OF THE REMAINS OF IVAN AND THERE IS
DISAGREEMENT ON THIS.  THE MODEL SPREAD INDICATES INCREASED
UNCERTAINTY ASSOCIATED WITH THIS PARTICULAR FORECAST.

SURPRISINGLY...THE SHIPS FORECASTS DECREASING SHEAR THROUGH 36 HOURS
BUT DOES NOT STRENGTHEN THE SYSTEM.  THE OFFICIAL FORECAST FOLLOWS
THE SHIPS GUIDANCE AND GRADUALLY INCREASES THE SYSTEM TO 60 KTS IN
4 DAYS.

FORECASTER JARVINEN

FORECAST POSITIONS AND MAX WINDS

INITIAL      18/0300Z 20.4N  72.2W    40 KT
 12HR VT     18/1200Z 20.9N  72.9W    40 KT
 24HR VT     19/0000Z 22.2N  73.5W    40 KT
 36HR VT     19/1200Z 24.3N  73.9W    40 KT
 48HR VT     20/0000Z 26.3N  74.0W    45 KT
 72HR VT     21/0000Z 29.0N  74.0W    50 KT
 96HR VT     22/0000Z 29.0N  74.0W    60 KT
120HR VT     23/0000Z 29.0N  74.0W    60 KT


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