307
FXUS64 KBRO 191140 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
640 AM CDT Sat Sep 19 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 636 AM CDT Sat Sep 19 2026

 - Daily low medium (20-40% or higher) chances of rain return next
   Monday and become region-wide by next Tuesday.

 - Temperatures ease off a few degrees from widespread areas of
   low 100s along/west I-69 E to mostly upper 90s by Tuesday.

 - Extreme risks of heat-related illnesses (level 4/4) are likely
   to continue for portions of the RGV/Rio Grande Plains while the
   rest of the region experiences moderate to major risks (level
   2/4 and 3/4).

 - A moderate risk of life-threatening rip currents continues
   through Saturday afternoon.

&&

.DISCUSSION...
Issued at 1040 PM CDT Fri Sep 18 2026

A bit of a dynamic and somewhat unsettled weather pattern sets up
across deep south Texas throughout the next 7 days or into late next
week. Subsidence and drier air associated with a 591-594+ dam high
pressure aloft over northeast Texas lowers moisture content tonight
through Sunday, cutting down on rain chances to, at most, a low
(15%) chance of an isolated shower or two over the southern
portions of the lower and mid RGV. Meanwhile, heights gradually
lower as the high becomes wedged between an upper level low
regressing to the eastern Gulf and as another pushes east from
the Intermountain West to the Plains by Monday. Following, the
combination of enhanced lift over the Gulf resulting from a series
of high pressure surges and a bit of nearby mid/upper level
trough vorticity advection along the southeastern periphery of a
high pressure aloft emerging over the Southern Plains re-enhances
moisture content and chances of rain. As a result, daily low to
medium (20-40% or higher) chances of rain along the daytime
seabreeze boundary expand from along/east US-281 next Monday to
most of the region by next Tuesday. Heavy rain and nuisance
flooding are possible as PWAT values increase, especially toward
the middle and later parts of the week. Still should note that
this is subject to change and will depend on the positioning and
strength of the high pressure aloft.

Widespread lower 100s across the Northern Ranchlands along/west of I-
69 E and across the RGV/Rio Grande Plains along/west US-281 are
expected Saturday through Monday, slightly cooling off to mostly the
upper 90s by Tuesday as clouds build. Additionally, areas of extreme
heat-related illnesses across portions of the RGV/Rio Grande Plains
continue through Monday and then become more limited to the lower
RGV by Tuesday while the rest of the region experiences moderate to
major risks. SPSs for heat indices of 108-111 F are possible as
well.

&&

.AVIATION...
(12Z TAFS)
Issued at 636 AM CDT Sat Sep 19 2026

Mostly clear skies with light and variable winds prevail across
Deep South Texas early this morning. Light winds are forecast to
increase and become easterly later this morning into the afternoon.
Light and variable winds are expected to return later this evening
into the overnight hours. VFR conditons will continue for the next
24 hours.

&&

.MARINE...
Issued at 1040 PM CDT Fri Sep 18 2026

Light to gentle, occasionally moderate, easterly to southeasterly
winds become gentle to moderate northeasterly to easterly on Tuesday
and mostly moderate by late week. Slight to moderate (2-4 ft) seas
ease to slight (1-2 ft) seas on Sunday before increasing back to
moderate later in the week. Low (15-30%) chances of rain tonight
decrease to 10% or less by Saturday afternoon. Low chances return on
Sunday, increasing to low to medium by Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             96  79  96  79 /  10   0  10   0
HARLINGEN               98  74  99  75 /  10   0  10   0
MCALLEN                101  78 101  79 /  10   0  10   0
RIO GRANDE CITY        102  77 102  77 /   0   0   0   0
SOUTH PADRE ISLAND      89  81  89  82 /  10  10  10  10
BAYVIEW/PORT ISABEL     94  78  95  78 /  10   0  10   0

&&

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

$$

SHORT TERM...65-Irish
LONG TERM....65-Irish
AVIATION...63-KC