[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 141457
TCDAT4

Tropical Storm Nicholas Discussion Number  10
NWS National Hurricane Center Miami FL       AL142021
1000 AM CDT Tue Sep 14 2021

Doppler weather radar data from Houston and Lake Charles, along with
surface observations, indicate that Nicholas has continued to weaken
while moving farther inland. The strongest winds recently reported
near the Texas and Louisiana coasts have been 33-35 kt at a TCOON
observing station near Sabine Pass, Texas. The strongest winds over
water south of southwestern Louisiana are based on Doppler radar
average velocities of 45-50 kt between 5000-7500 ft. Based on these
wind data, the initial intensity has been lowered to 40 kt. The
estimated central pressure of 1002 mb is based on nearby surface
observations in the Houston metropolitan area. Further weakening is
expected as Nicholas moves farther inland due to frictional
effects, entrainment of very dry mid-level air from the southern
Plains, and increasing southwesterly to westerly shear. The latter
condition is expected to cause the low- and upper-level circulation
to decouple in about 24 hours, which will hasten the weakening
process. No significant changes were made to the previous intensity
forecast, and Nicholas is now expected to become a tropical
depression by tonight and degenerate into a remnant low by
late Wednesday.

Nicholas is now moving northeastward or 050 degrees at a slower
forward speed of 5 kt. The cyclone should gradually turn toward the
east-northeast by tonight, and move eastward more slowly on
Wednesday and Thursday. It is possible that Nicholas could stall
over southwestern or central Louisiana as the low-level steering
flow collapses.  The new NHC track forecast is similar to but
slightly slower than the previous advisory tack.

Although the winds associated with Nicholas will be weakening,
heavy rainfall and a significant flash flood risk will continue
along the Gulf Coast during the next couple of days.


Key Messages:

1. Heavy rainfall will impact areas from the upper coast of Texas,
across Louisiana, southern Mississippi, far southern Alabama and the
western Florida Panhandle through Thursday. Significant rainfall
amounts are expected, potentially resulting in areas of
life-threatening flash and urban flooding across these areas.  Minor
to isolated major river flooding is also possible in smaller river
basins and urban areas.

2. There is the danger of life-threatening storm surge inundation
along the coast of Texas from Port Bolivar to Sabine Pass.
Residents in these areas should follow any advice given by local
officials.

3. Tropical storm conditions are expected to continue along the
Louisiana coast into this afternoon. Tropical storm conditions
in the warning area across the upper Texas coast will diminish this
afternoon as Nicholas moves farther to the northeast.


FORECAST POSITIONS AND MAX WINDS

INIT  14/1500Z 29.6N  95.3W   40 KT  45 MPH...INLAND
 12H  15/0000Z 30.1N  94.7W   30 KT  35 MPH...INLAND
 24H  15/1200Z 30.4N  93.9W   25 KT  30 MPH...INLAND
 36H  16/0000Z 30.4N  93.2W   25 KT  30 MPH...INLAND
 48H  16/1200Z 30.5N  92.8W   15 KT  15 MPH...INLAND
 60H  17/0000Z 30.9N  92.8W   15 KT  15 MPH...POST-TROP/REMNT LOW
 72H  17/1200Z...DISSIPATED

$$
Forecaster Stewart
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