[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 130259
TCDAT4

Tropical Storm Nicholas Discussion Number   3
NWS National Hurricane Center Miami FL       AL142021
1000 PM CDT Sun Sep 12 2021

Nicholas is not yet a well-organized tropical cyclone, with little
evidence of convective banding features on satellite imagery.
Observations from the Air Force Hurricane Hunter aircraft indicate
that the center is still not very well-defined, and appears to have
reformed again, this time farther south.  Data from the aircraft
indicate that the central pressure has not changed much since
earlier today, and the maximum winds remain near 35 kt.  This is
above the latest Dvorak intensity estimates from TAFB and SAB.

Nicholas will be traversing very warm waters during the next day or
so, and within a moist, unstable atmosphere.  These factors would
favor strengthening.  However, moderate southwesterly shear
associated with an upper-level trough over northern Mexico could be
an inhibiting factor for strengthening.  In spite of the shear,
the GFS model forecasts the system to strengthen while it nears
the Texas coast.  The official intensity forecast is at the upper
end of the current model guidance.  Given the uncertainties in the
future strength of Nicholas, a Hurricane Watch is in effect for a
portion of the Texas coast.

The current location of Nicholas is quite uncertain since the
aircraft-reported center position is within a broad area of light
winds and is well south of most of the deep convection.  Although
the fixes show little motion this evening, based on the model
predictions, it appears likely that the center will shift or re-form
significantly northward as early as Monday morning.  This is at
least partially accounted for in the latest NHC track forecast, but
some northward adjustments are possible over night.  The storm
is expected to move toward a weakness in the subtropical ridge
during the next 36 hours or so.  The track guidance and the model
consensus has shifted eastward somewhat since the earlier advisory
package.  This has necessitated an eastward shift in the official
track, and a northeastward extension of the watches and warnings.


Key Messages:

1.  Periods of heavy rainfall are expected to impact portions of the
Texas and Louisiana coasts through the middle of the week.
Significant rainfall amounts are possible, potentially resulting in
areas of considerable flash and urban flooding, especially in highly
urbanized metropolitan areas. Isolated minor to moderate river
flooding is also expected.

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

3. Nicholas is forecast to approach the middle Texas coast as a
strong tropical storm late Monday and early Tuesday, and could be
near hurricane intensity if it moves to the right of the forecast
track and remains over water longer. Tropical storm conditions are
expected along portions of the middle Texas coast beginning Monday
afternoon, with hurricane conditions possible from Port Aransas to
Freeport late Monday and Monday night.

4. Tropical storm conditions are expected along portions of the
northeastern coast of Mexico and the coast of south Texas beginning
Monday morning.


FORECAST POSITIONS AND MAX WINDS

INIT  13/0300Z 22.5N  95.5W   35 KT  40 MPH
 12H  13/1200Z 24.7N  96.5W   45 KT  50 MPH
 24H  14/0000Z 27.0N  96.5W   50 KT  60 MPH
 36H  14/1200Z 28.6N  96.1W   55 KT  65 MPH...NEAR THE COAST
 48H  15/0000Z 29.9N  95.4W   45 KT  50 MPH...INLAND
 60H  15/1200Z 30.4N  94.8W   40 KT  45 MPH...INLAND
 72H  16/0000Z 31.0N  94.0W   30 KT  35 MPH...INLAND
 96H  17/0000Z 31.7N  92.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  18/0000Z...DISSIPATED

$$
Forecaster Pasch
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