[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 201200
TCDAT3
TROPICAL STORM LISA SPECIAL DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM EDT MON SEP 20 2004

VARIOUS SATELLITE SOURCES AND INTENSITY ESTIMATES INDICATE THAT
TROPICAL DEPRESSION THIRTEEN HAS BECOME BETTER ORGANIZED AND HAS
STRENGTHENED. THE FIRST FEW VISIBLE SATELITE IMAGES INDICATE A
BANDING EYE FEATURE IS TRYING TO DEVELOP...AND A 20/0955Z SSMI
OVERPASS REVEALED A SMALL MID-LEVEL EYE WAS PRESENT. SUCH FEATURES
ARE TYPICALLY CHARACTERISTIC OF 45-55 KT TROPICAL CYCLONES. THE
INITIAL INTENSITY ESTIMATE OF 45 KT IS ALSO SUPPORTED BY A 20/0902Z
UW-CIMSS AMSU PRESSURE ESTIMATE OF 999.1 MB. THEREFORE...THE
DEPRESSION IS BEING UPGRADED TO TROPICAL STORM LISA.

THE INITIAL MOTION ESTIMATE IS 275/10.  THERE IS NO CHANGE TO THE
PREVIOUS TRACK FORECAST OR REASONING. THIS SPECIAL ADVISORY IS ONLY
TO INDICATE THE INCREASE TO TROPICAL STRENGTH...AND AN INCREASE IN
THE INTENSITY FORECAST.

LISA IS A SMALL AND RATHER COMPACT TROPICAL CYCLONE. AS SUCH...IT IS
SUSCEPTIBLE TO SHARP CHANGES IN INTENSITY...BOTH STRENGTHENING AND
WEAKENING. THE VERTICAL SHEAR IS FORECAST TO REMAIN AROUND 10 KT OR
LESS FOR THE NEXT 24 HOURS...SO STRENGTHENING TO HURRICANE
INTENSITY IS FORECAST. AFTER THAT...LOW TO MODERATE VERTICAL SHEAR
IS EXPECTED TO POSSIBLY PUT A CAP ON THE INTENSIFICATION TREND...SO
ONLY SLOW STRENGTHENING IS FORECAST IN THE 24-48 HOUR PERIOD...WITH
A LEVELING OFF OF THE INTENSITY AFTER THAT. HOWEVER...IF LISA TAKES
A MORE SOUTHERLY TRACK TO THE LEFT OF THE OFFICIAL FORECAST TRACK
...THEN THE SHEAR WILL BE LESS AND MORE STRENGTHENING WOULD BE
POSSIBLE THAN WHAT THE OFFICIAL INTENSITY FORECAST IS INDICATING.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      20/1200Z 13.5N  35.4W    45 KT
 12HR VT     20/1800Z 13.6N  36.4W    55 KT
 24HR VT     21/0600Z 14.1N  38.2W    65 KT
 36HR VT     21/1800Z 14.5N  39.7W    70 KT
 48HR VT     22/0600Z 15.0N  41.5W    75 KT
 72HR VT     23/0600Z 17.0N  45.0W    75 KT
 96HR VT     24/0600Z 18.0N  48.0W    75 KT
120HR VT     25/0600Z 18.5N  51.0W    75 KT


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