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A few swirls trying to earn an Invest tag in the final days of the 2021 Season. Their environment is not ideal for development.
Days since last H. Landfall - US: Any 76 (Nicholas) , Major: 92 (Ida) Florida - Any: 1146 (Michael) Major: 1146 (Michael)
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#1061450 (Received by flhurricane at: 10:38 AM 13.Sep.2021)

Tropical Storm Nicholas Discussion Number 6
NWS National Hurricane Center Miami FL AL142021
1000 AM CDT Mon Sep 13 2021

Doppler radar data from Brownsville and Corpus Christi, Texas, along
with reconnaissance aircraft flight-level wind data, indicate that
Nicholas' inner-core structure has undergone some radical changes
since the previous advisory. The earlier near-eyewall pattern
dissipated a few hours ago, and has been replaced with what appears
to be an ongoing reformation of a new center abut 90 nmi
north-northeast of the old center. The aircraft recently found a
pressure of 1000 to 1002 mb with the dissipating original center,
while Doppler radar velocity data show a pronounced mid- to
upper-level circulation forming farther north as previously
mentioned. The Air Force Reserve Hurricane Hunter aircraft is going
to be concentrating its reconnoiter mission in Nicholas'
northeastern quadrant to see if reformation of the low-level center
is occurring beneath the mid-level circulation noted in radar data.
The initial wind speed remains 50 kt based on recent aircraft 850-mb
flight-level winds of 59 kt, which equates to about 47 kt equivalent
surface winds.

The initial motion is an uncertain 005/10 kt due to the erosion and
ongoing reformation of the center. Despite the recent inner-core
erosion, the latest NHC model guidance remains in fairly good
agreement on Nicholas moving northward through a weakness in the
subtropical ridge. The GFS model has been performing exceptionally
well with predicting the recent erosion and more northward
reformation of the Nicholas' center. The new NHC track forecast is
similar to but slightly east or right of the previous advisory
track, and lies along the eastern edge of the track consensus model
envelope, which is to the left of the GFS track prediction.

Although the inner-core convective pattern has been disrupted,
recent trends in the radar data suggest that a new center should
reform farther northeast into the convective cloud shield. The
latest GFS- and ECMWF-based SHIPS shear analyses indicate that
westerly shear of near 20 kt is allegedly affecting Nicholas.
However, water vapor satellite imagery suggests that the upper-level
shear vector is actually from a south-southwesterly direction, which
is more along than across the cyclone's forward motion, thus
reducing the magnitude and negative effects of the vertical wind
shear. Therefore, strengthening is still expected until landfall
as Nicholas continues to move over slightly warmer Gulf waters. It
is possible that Nicholas could become a hurricane just before
landfall, and that's the reason for the northeastward extension of
the hurricane watch area. Nicholas should rapidly weaken after
landfall due to increased frictional effects, strong southwesterly
shear, and entrainment of mid-level dry air, resulting in
degeneration into a tropical depression by late Tuesday and a
remnant low on Wednesday. Otherwise, no significant changes were
made to the previous advisory intensity forecast.

Key Messages:

1. Heavy rainfall will impact portions of the Texas and Louisiana
coasts through the middle of the week. Significant rainfall amounts
are possible, potentially resulting in areas of life-threatening
flash and urban flooding, especially in highly urbanized
metropolitan areas. Minor to isolated 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 Sabine 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 by this evening, and could be near hurricane
intensity at landfall. Tropical storm conditions are expected
along portions of the middle Texas coast beginning this afternoon,
with hurricane conditions possible from Port Aransas to San Luis
Pass by late afternoon through tonight.

4. Tropical storm conditions are expected along portions of the
coast of south Texas into the afternoon.


INIT 13/1500Z 26.4N 96.8W 50 KT 60 MPH
12H 14/0000Z 27.5N 96.7W 60 KT 70 MPH
24H 14/1200Z 29.1N 96.3W 45 KT 50 MPH...INLAND
36H 15/0000Z 30.2N 95.4W 30 KT 35 MPH...INLAND
48H 15/1200Z 31.0N 94.0W 25 KT 30 MPH...INLAND
60H 16/0000Z 31.5N 92.5W 20 KT 25 MPH...INLAND
72H 16/1200Z 32.0N 91.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 17/1200Z...DISSIPATED

Forecaster Stewart