[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 121502
TCDAT4

Tropical Storm Nicholas Discussion Number   1
NWS National Hurricane Center Miami FL       AL142021
1000 AM CDT Sun Sep 12 2021

Showers and thunderstorms associated with a broad area of low
pressure over the southern Bay of Campeche have increased overnight
and very recently become better organized with a loose band of
convection around the northeastern portion of the circulation. An
Air Force Reserve reconnaissance aircraft that has been
investigating the system has found 44-kt flight-level winds and
SFMR winds that support a 35-kt initial intensity.  Based on the
recent increase in organization and the 35-kt initial intensity,
advisories are being initiated on Tropical Storm Nicholas, the
fourteenth named storm of the Atlantic hurricane season.

The storm is located within an environment of moderate
south-southwesterly vertical wind shear, over warm waters, and in a
moist and unstable atmosphere. These conditions should allow gradual
strengthening over the next 24 to 48 hours.  The NHC intensity
forecast follows suit and calls for gradual strengthening until
the system reaches the coast of Texas.  The official wind speed
forecast is near the higher end of the guidance in best agreement
with the SHIPS statistical guidance, the HFIP corrected consensus,
and the HWRF.  In this case, the intensity forecast is highly
dependent on eventual track of the system.  A track to the east of
the NHC forecast could result in a lower wind shear environment
and slightly more time over water for the system to strengthen.
Conversely a track to the west of the forecast track would result
in the system interacting with land much sooner.

Since the system is still in its formative stage the initial motion
estimate is a somewhat uncertain 330/11 kt.  A north-northwestward
motion around the western portion of a mid-level ridge that is
sliding east near the coast of the Carolinas, should continue to
steer Nicholas in that direction for the next 24 to 48 hours.
After that time, steering currents weaken and the cyclone is
expected to move slowly north-northeastward between a couple of
mid-level ridges located to the east and west of Nicholas.  The
track guidance generally agrees with this overall scenario but
there is some cross-track spread with the UKMET along the left side
of the guidance envelope taking the storm into northeastern Mexico,
while the GFS, HWRF, and HMON are along the right side.  The NHC
track is near the various consensus models and both the EC and GFS
ensemble means.

Key Messages:

1. Tropical storm conditions are expected along portions of the
northeastern coast of Mexico and the coast of south Texas
beginning on Monday.  Nicholas is forecast to approach the middle
Texas coast as a strong tropical storm on Tuesday, and tropical
storm conditions are possible along portions of the middle and upper
Texas coasts late Monday night and Tuesday.

2. There is the possibility of life-threatening storm surge along
the coast of Texas from the Mouth of the Rio Grande to High Island.
Residents in these areas should follow any advice given by local
officials.

3.  Periods of heavy rainfall are expected to impact portions of the
Texas and Louisiana coasts today through the middle of the week.
Significant rainfall amounts are possible, potentially resulting in
areas of flash, urban, and isolated river flooding.


FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 20.5N  94.8W   35 KT  40 MPH
 12H  13/0000Z 21.9N  95.7W   40 KT  45 MPH
 24H  13/1200Z 24.1N  96.6W   45 KT  50 MPH
 36H  14/0000Z 26.4N  96.9W   50 KT  60 MPH
 48H  14/1200Z 28.2N  96.5W   55 KT  65 MPH
 60H  15/0000Z 29.4N  95.9W   40 KT  45 MPH...INLAND
 72H  15/1200Z 30.3N  95.2W   30 KT  35 MPH...INLAND
 96H  16/1200Z 31.0N  94.8W   25 KT  30 MPH...INLAND
120H  17/1200Z 32.0N  94.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown
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