September 2021: Hurricane Nicholas

[Andrew]

00z Euro is much different compared to the previous runs. It stalls it out over Southern Texas with Corpus and regions around there seeing the flooding risk.

EDIT: Eventually by day 4 the system shifts north

[don]

0Z EURO shows some pretty high rainfall amounts...

[Cpv17]

I like this run of the Euro. Gives me about 5-7”. Sign me up!

[Andrew]

00Z Euro is a lot slower overall and we don't see a lot of the heavy rain across SE Texas until Tuesday and Wendesday

[Goomba]

[Cpv17]

We now have invest 94L.

[Scott747]

Significant change in the latest TWO -

1. Disorganized showers and thunderstorms over portions of Central
America, southeastern Mexico, and the adjacent waters of the
northwestern Caribbean Sea and southern Gulf of Mexico are
associated with a tropical wave interacting with an upper-level
trough. Upper-level winds over the western Gulf of Mexico are
expected to become more conducive for development over the weekend,
and a tropical depression is likely to form on Sunday or Monday
while the system moves northwestward and then northward near the
coast of northeastern Mexico. Further development of this system
will be possible through the middle of next week if it remains over
water, and interests along the western and northwestern Gulf coast
should monitor the progress of this system.

6z GFS continues the weaker trend after that 18z run. Strong reflection early on that never really fully organizes as it moves n along the coastline from Tampico towards Matagorda Bay and eventually nne towards the border. Bulk of the rain remains just along the immediate coastline and over sw la.

6z ICON with a weak ts into Matagorda Bay late on Monday.

[redneckweather]

This will be a rainmaker for Texas, not much else. Kind of look at at it as some of those rainy days we had back in May and June.

Come on cold fronts!

[srainhoutx]

Saturday morning weather briefing from Jeff:

Tropical cyclone formation likely over the western Gulf of Mexico late this weekend or early next week.

Heavy to excessive rainfall possible over portions of SE TX early next week.

The tropical wave over the Yucatan continues to progress westward and will enter the Bay of Campeche later today. As upper level winds gradually become more favorable for development a tropical depression or storm may form late Sunday into Monday. There is decent agreement with the global forecast models that a surface low will from, but where exactly remains in question and this is important given the potentially close proximity to the eastern coast of MX or S TX and if the low if offshore on moves onshore. The majority of the models and their respective ensembles keep any surface low just off the western Gulf coastline. Steering flow over the western Gulf early next week will be generally from south to north with high pressure over the eastern Gulf and FL and a height field weakness across TX ENE into the lower MS Valley. This supports track solutions toward the NNW, N or NNE or generally from the SW Gulf toward the NW Gulf Monday into Tuesday.

The hurricane center remain at 80% probability for tropical cyclone formation over the next 5 days.

Rainfall:

Regardless of tropical cyclone formation a large mass of tropical moisture over the Gulf of Mexico will be approaching and moving onto the TX coast starting on Sunday. Significant rainfall will be possible in the Mon-Wed time period with excessive short term rainfall rates of 2-4 inches per hour possible under any banding, training, or clustering of the stronger cells. It is likely to be a few very wet days Mon-Wed, especially near the coast. Models continue to show varying degrees of inland extend of the heavy rainfall and this appears to be strongly tied to the formation and track of any surface low up from our S/SW. At this time, with the uncertainty on where a surface low may develop, will continue to focus the heaviest rains near the coast with a sharp inland gradient to the NW away from the coast.

Widespread rainfall amounts of 2-4 inches will be common over much of the area with much higher totals of 5-10 inches most likely near the coast and isolated totals in certain areas could be higher than 10 inches. Given the deep tropical air mass that will be in place by late Sunday, hourly rainfall rates of 2-4 inches per hour will be possible under the heavier cells into next week. While grounds are generally dry over the area, the magnitude of the rainfall in a short period of time could result in significant run-off generation especially over urban areas. Flooding concerns will increase as grounds become saturated early next week.

Winds/Seas/Tides:

There still remains a fair amount of uncertainty on where any surface low forms over the western Gulf and what effect son winds, seas, and tides that may have. For now will continue with developing easterly and southeasterly winds today into Sunday and increasing into the 15-25kt range with seas building 6-10ft offshore by late Sunday into Monday. Larger swells moving onto the coast will likely lead to some wave run-up and minor coastal flooding at times of high tides from late Sunday into early next week.

Continue to closely monitor forecasts for changes over the next 48-72 hours.

[tireman4]

000
FXUS64 KHGX 111118
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
618 AM CDT Sat Sep 11 2021

.AVIATION [12Z TAF Issuance]...

Winds remain light and variable across the region, but will
become easterly around 10 knots later in the morning hours. Winds
will become light and variable once again on Saturday night. FEW
to SCT clouds around 5,000 ft will roll in from the south
throughout the day. VFR conditions will prevail throughout the TAF
period.

Batiste

&&

.PREV DISCUSSION /Issued 449 AM CDT Sat Sep 11 2021/...

.SHORT TERM [Through Sunday Night]...
Guess what`s back....back again! 50s are back....tell a friend! For
the second night in a row we have upper 50s on the map, this time
Conroe joined the party with a temperature of 57 degrees as of 3am
(their first time in the 50s since May 15th). Dewpoints in the
50s/60s continue to prevail across the CWA, so this morning will be
another pleasant and dry one before we start the transition into a
wet pattern. Satellite-derived total PW show that while most of the
CWA is living luxuriously with 0.6"-0.7" PW values, just off the
coast PW values are steadily climbing as moisture begins to
increase. By this afternoon, PW values along the coast and in our
southwestern counties will range from 1.2"-1.5". With weak
shortwaves still wrapping around the upper-level high over AZ/North
TX, scattered showers/thunderstorms will be able to move further
inland this afternoon. The highest PoPs are offshore, along the
coast, and in our southwestern counties. With increasing moisture
comes an increase in overnight temperatures as well, so expect
Saturday night`s lows to be 4-6 degrees warmer especially for
locations south of I-10.

The NHC is monitoring a tropical wave that will soon emerge into the
Bay of Campeche that now has a high chance of formation over the
next two days (70%). A tropical depression is likely to form on
Sunday at the earliest as upper-level winds are becoming more
favorable for development to occur. Uncertainty remains on exactly
how fast this develops and its track, but there is model consensus
on a large surge of moisture (PW values 2+") pushing into Southeast
TX on Sunday morning/afternoon. PoPs steadily increase from the
coast and expanding northward throughout the day as this moisture
pushes in. For most of the day on Sunday, PoPs and cloud coverage
will be highest to the south of I-10. As a result, high temperatures
on Sunday south of I-10 will be relegated to the upper 80s with 90s
north of I-10. PoPs continue to increase heading into Sunday night
as the GFS, NAM, and Canadian are picking up on a developing jet
streak over the CWA. Exact timing and intensity of this jet streak
is a little uncertain with the NAM and Canadian being the
quicker/stronger solutions for setting up upper-level divergence, so
for now keeping PoPs in line with the NBM. Additionally, the WPC has
outlined the counties south of and along I-10 in a marginal risk for
excessive rainfall for Sunday. Locally heavy rainfall will be
possible beginning on Sunday night, so be sure to stay up to date
with the latest forecasts.

Batiste

&&

.LONG TERM [Monday Through Saturday]...
Monday:
Showers and thunderstorms should be ongoing across coastal
sections and offshore Monday morning in association with a zone of
moderate to strong llvl convergence along a trof/easterly wave
axis, mid level vorticity maxima and a fairly pronounced region of
diffluent flow aloft. With high PW`s (2.4-2.6") in place, heavy
tropical downpours are a good bet...capable of producing several
inches of rain in a very short time period. On ***average*** 2-4"
of rain can generally be expected south of a Matagorda Bay-Liberty
line through Monday night & less so the further inland one goes.
That said, there is considerable concern that for several days
models have been producing signals for embedded/more localized
values double or even triple that. What we`re not confident with
is pinpointing the exact locations, if any, where any of these
potential more excessive values might occur...be it offshore or
just inland a county or two.

Tuesday-Thursday:
Eyes on the Gulf. Conditions are favorable for the tropical wave
currently moving wwd across the Yucatan to develop into a tropical
depression at some point Sun-Mon in the Bay of Campeche or
western Gulf. General steering flow should generally favor a
northward movement along the coast of Mexico toward Texas. Until
(if and/or when), this system becomes better organized it is too
early for specifics (timing, intensity, impacts, etc). What we do
know is that the 00z ECMWF positions a low pressure area about 40
miles west of Corpus Christi Tuesday morning and generally closer
to its respective ensemble suite. GFS depicts a low about the same
latitude, but about 90 miles offshore Corpus like its slightly
eastward ensemble suite. Obviously one over water would be more of
a concern...but we don`t even know if/when a closed circulation
will develop in the first place. In the meantime, what we do know
is that we`ll continue to see Gulf moisture continuing to flow
inland well into midweek...continuing the rain chances.

Fri-Sat:
Dependent on Tue-Thur wx evolution. Indications are wx will begin
to settle down, but will have daily chances of sct precip across
parts of the area.

Summary:
Seven day forecast rain totals should range from 1-3" across nw
parts of the CWA to 5-10+" at the coast and offshore. Vast
majority of the region can initially absorb a decent amount of
rain...so long as it`s spread out and doesn`t all fall at once. As
the ground becomes saturated, flood/flash flood concerns go up
with subsequent rains and runoff. High rain rates in a short time
period are always a FF concern, esp metro areas, regardless of
ground condition. 47

&&

.MARINE...
Winds/seas will be on an upward trend this weekend. Have caution
flags flying in the 20-60nm group for moderate east winds. Will
probably need to eventually expand those northward, or upgrade, heading
into Sunday afternoon and night as gradient further tightens.
Unsettled weather, with several rounds of showers and thunderstorms,
can be expected beginning on Sunday and likely continuing well
into next week. Mariners should closely monitor the latest
forecasts as there is increasing potential for some tropical
development in the Bay of Campeche and western Gulf late this
weekend. See "Tuesday-Thursday" portion above for uncertainties.
Dependent on what, if anything, evolves we`ll need to keep an eye
on the tide levels Sun-Wed and potential for some coastal flooding
around high tide times. Not sure there will be many swimmers at
the beaches during this time period considering the wx, but there
will be a high risk of rip currents. 47

&&

.FIRE WEATHER...
North of Harris County, enough dry air remains in place to drop RH
values into the upper 20%/low 30% range in the afternoon hours.
Winds today will mainly be light and easterly once again with
moderate winds closer to the coast. Moisture will steadily increase
from the coast and expanding northward on Saturday afternoon as we
transition into a wet pattern that extends into next week.

Batiste

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL) 93 66 93 73 87 / 0 0 20 20 60
Houston (IAH) 92 71 90 74 85 / 0 0 50 50 80
Galveston (GLS) 88 80 86 77 84 / 20 30 80 80 90

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...None.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 4 PM CDT this
afternoon for the following zones: Waters from Freeport to
Matagorda Ship Channel TX from 20 to 60 NM...Waters from
High Island to Freeport TX from 20 to 60 NM.

[don]

94L 12Z tropical models.

[srainhoutx]

Today marks the 60th Anniversary of Hurricane Carla making landfall.

[don]

12Z ICON showing 94L becoming a tropical storm making landfall around Matagorda.

[Cromagnum]

We thinking weak to moderate tropical storm here with a bucket of rain?

[weatherguy425]

Here is a great tweet thread, laying out the envelope of scenarios. (Hopefully these attach in the right order - lol)

EDIT| I guess start at the bottom and read up.

[Scott747]

12z is trying to develop a little earlier than the 6z e of Veracruz.

Much stronger by early monday afternoon approaching hurricane strength e of Tampico.

[don]

Yep,its a lot more organized than the previous run so far.

[Cromagnum]

Waiting for that trough to be more progressive and keep the boundary all the way just off the coast .

[Scott747]

Moving n to nne offshore between Brownsville and Corpus at 998 early Tuesday

Beginning to deepen quickly Tuesday morning

Early Tuesday afternoon moving nne offshore of sargent at 991

Early Tuesday evening offshore of San Luis/Galveston at 996

Early Wednesday morning moving ne towards the border at 996

Landfall around Cameron as a weak ts Wednesday morning

[Cpv17]

This is the usual GFS right bias Euro left bias. Split the difference down the middle and there you go.