-- Discussion containing changed information from previous version are highlighted. --
467
FXUS64 KBRO 230857
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
357 AM CDT Mon Sep 23 2024

...New SHORT TERM, LONG TERM, MARINE...

.SHORT TERM...
-- Changed Discussion --
(Today through Tuesday)
Issued at 347 AM CDT Mon Sep 23 2024

The first full day of Autumn 2024 might still be called "Hotumn"...as
temperatures will be more like late August day and night and
combined with continued tropical humidity it will feel like 100 to
108. Similar temperatures will be had Tuesday...all courtesy of a
continued flat subtropical 500 mb ridge that remains across
northern Mexico through the Valley and into the western Gulf.
Fortunately, the strength of the ridge is not like we saw in
August and with lowering sun angle and lengthening nights
conditions are not as sweltering...but that doesn`t mean it feels
anything close to relief across the southern tip of Texas.

As for sensible weather...Sunday was largely dry, as the sea breeze
had little deep moisture to work with.  Today shows a hint of
slightly higher deep layer moisture easing in from the east...but
only in the 800-600 mb layer and the increase is subtle.  With no
pronounced forcing, the best we`ll do is isolated (10-20 percent)
rain chances, jumping inland along the sea breeze but likely
petering out before reaching along/west of Brooks/Hidalgo.

Skies clear out again tonight with near calm winds, but similar
temperatures a few degrees above seasonal norms by early Tuesday.  A
possible slug of deeper moisture may reach the Lower Texas coast
courtesy of an embedded weak short wave that attempts to slide west.
However, that wave/shear axis may hang up offshore, and models hint
at deeper moisture doing similar. By late Tuesday, we turn our
attention to a deepening 500 mb trough diving southward through the
eastern Plains, which should enhance rain chances beyond this
period.

Until then, sensible weather may feature better coverage along the
coast to begin Tuesday before it, too, jumps inland along the sea
breeze beginning in early afternoon.  Thereafter, the usual diurnal
rules apply...and locations generally along/east of IH-69E/US 77
should see an end to any convection by mid afternoon.  Have modified
the blended forecast to account...and be similar to this afternoon.
That said, the additional moisture should favor slightly higher
coverage of afternoon rain...though still below what the model
blends are advertising which seems overcooked given deterministic
solutions as well as 36-48 hour precipitation depictions from the
convective-allowing models (CAMs) which are more "typical" isolated
to scattered conditions.

Finally...we`ll be watching tide conditions especially at South
Padre Island today through Tuesday. The first of the season`s "King"
tides have arrived and peak near 0.7 feet above normally high
ground through Tuesday. Water levels are already running about
0.65 feet above predicted values.  Expected values today and
tomorrow are in the 1.2 to 1.4 feet above normally high ground and
this may push water levels up on the beach, reducing available beach
to use.  That said, with wave/swell energy very limited, sea water
should not reach the dunes...but we may need to consider a Coastal
Flood Statement as early as this morning if visual conditions
warrant one.
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&&

.LONG TERM...
-- Changed Discussion --
(Tuesday night through Sunday)
Issued at 347 AM CDT Mon Sep 23 2024

We look to begin the long term period with an upper level trough
situated across the Central US. As the trough pushes further east,
the southern portion looks to break off and develop a closed low
over the ArkLaTex region Thursday. Both the GFS ans ECMWF have
this closed low interacting with a possible tropical system late
in the week, pushing the closed low southwest deeper into Texas.

At the surface, PWAT values between 1.6 and 1.9 inches and CAPE
values around 1000 J/kg could support showers and thunderstorms
Developing Wednesday and Thursday. A stationary front across
Central Texas and and the daily sea breeze could provide forcing
to support isolated to scattered showers and thunderstorms
Wednesday. Recent runs of the GFS and ECMWF have the frontal
boundary pushing south early Thursday, with isolated to scattered
showers and thunderstorms possible along the front. Dry air behind
the front looks to limit additional rain chances through the
remainder of the period.

High temperatures look to be in the low to mid 90s Wednesday then
falling to the upper 80s to low 90s with the frontal passage
Thursday. High temperatures look to return to the low to mid 90s
Friday, and remain there through the remainder of the period.
Likewise, low temperatures look to range from the low to mid 70s
Tuesday and Wednesday nights, before dropping into the 60s
Thursday night. Low temperatures look to return to the low to mid
70s over the weekend.

The combination of Frontal passage and the arrival of long period
swell on Thursday will likely produce hazardous beach conditions
Thursday and Friday. There will likely be a high risk of Rip and
Longshore currents, and some minor coastal flooding cant be ruled
out.
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&&

.AVIATION...
(06Z TAFS)
Issued at 1249 AM CDT Mon Sep 23 2024

Another quiet weather day is on tap for landings/takeoffs for
this Monday...with perhaps a slight uptick in the potential for
isolated early afternoon showers or even a rogue thunderstorm as
mid level moisture gets a slight boost across the lower Valley.
Confidence is low at this point as dry air is pretty stout above
the usual cumulus/stratocumulus deck at the lifting condensation
level which rises from high MVFR through low VFR. Across the
mid/upper Valley (McAllen/Miller area) the very dry air layer
holds through at least 4 PM. For now...have left Brownsville out
of mentionable rain but included a VCSH for Harlingen as the sea
breeze may coincide with the slight uptick in moisture.

As for clouds...heating/moisture percolation should pop the usual
cumulus by 9 or 10 AM in the lower Valley and a little later for
McAllen. Added periodic broken conditions based on Sunday`s
observations but mostly in low VFR conditions. Should see some
isolated congestus but that`s about it. By late afternoon in the
lower Valley and just after sunset in McAllen, skies should clear
once again.

As for winds...guidance a touch low following the afternoon sea
breeze enhancement and based on Sunday have nudged speeds up a few
knots before laying down to light by or just after sunset.

&&

.MARINE...
-- Changed Discussion --
Issued at 347 AM CDT Mon Sep 23 2024

Today through Tuesday...Winds (easterly) and seas will be light and
slight, respectively, with surface high pressure locked into the
northern half of the Gulf. However, boating may become a bit more
difficult especially Tuesday as shower coverage increases to
scattered to numerous with isolated thunderstorms. Lightning and
briefly torrential rains along with some gusty winds and choppy
waters will be the primary concerns...favoring the waters beyond 10-
20 nm out.

Tuesday night through Sunday...Generally favorable marine
conditions look likely through Wednesday night as light to
moderate winds and slight seas continue along the Lower Texas
Coast. Conditions look to deteriorate Thursday, with the passage
of a cold front and the arrival of swell from a possible tropical
system in the Eastern Gulf. This combination will likely result in
confused seas and as northerly winds and waves combine with
easterly swell. Small Craft Should Exercise Caution headlines and
Small Craft Advisories will likely be needed for the Gulf waters
Thursday and Friday. Additionally, winds could approach criteria
for Small Craft Should Exercise Caution headlines on the Laguna
Madre with the frontal passage on Thursday. Favorable marine
conditions look to return Saturday as light to moderate winds and
slight seas persist through the remainder of the period.
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&&

.PRELIMINARY POINT TEMPS/POPS...
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BROWNSVILLE             93  78  93  76 /  20  10  30  30
HARLINGEN               94  74  94  73 /  20  10  30  10
MCALLEN                 97  78  97  77 /  10   0  30  20
RIO GRANDE CITY         95  75  95  75 /  10  10  20  20
SOUTH PADRE ISLAND      88  81  88  80 /  20  20  40  30
BAYVIEW/PORT ISABEL     90  76  90  76 /  20  10  40  20
-- End Changed Discussion --

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

SHORT TERM...52-Goldsmith
LONG TERM....60-BE
AVIATION...52-Goldsmith