Severe Thunderstorm Warning 28, NWS Brownsville, TX

Area Forecast Discussion
National Weather Service Brownsville TX
103 PM CDT Fri May 22 2026

...New DISCUSSION, AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1248 PM CDT Fri May 22 2026

Key Messages:

 * Isolated showers and thunderstorms could impact the Western
   Ranchlands this evening as convection fires off the Sierra
   Madre.

 * A Flood Watch is in effect until Monday morning. There is a
   chance of isolated to scattered flash flooding in areas that
   receive heavier rainfall on Saturday and Sunday.

 * Warm and humid conditions are expected through next weekend
   with Minor (level 1 of 4) and Moderate (level 2 of 4) Heat
   Risks expected to impact the area.

 * A moderate risk of rip currents continues through Saturday afternoon.

&&

.DISCUSSION...
Issued at 1248 PM CDT Fri May 22 2026

A deeply moist atmospheric profile remains in place throughout the
weekend, due to a combination of ample Gulf surface moisture and
Pacific moisture aloft, which is being carried into Deep South Texas
across Mexico due to persistent westerly 500 mb flow. Resultantly,
abnormally high PWAT values (between 1.6 and 2.2 inches) are
expected over the region, with the highest values being observed on
Saturday.  Shortwave activity is also expected over the next few
days, which will make the atmosphere unsettled and prone for
convection to form. Since the atmospheric profile is so moist,
convection that forms this weekend will be persistent and efficient
rainmakers, which could result in high precipitation amounts and
possibly isolated to scattered flash flooding across portions of
Deep South Texas.  A Flood Watch is in effect until Monday morning.

The remainder of the afternoon today is expected to be relatively
dry and rain free, but convection is expected to form off the Sierra
Madres after sunset which could bring a few showers and
thunderstorms to the western portion of the CWA during the evening
hours. Overall, PoPs are expected to remain relatively low overnight
(less then 30 percent), before increasing to 50 to 70 percent
tomorrow, as more widespread convection is expected to form with the
main shortwave disturbance. The higher PoPs will shift to the
eastern counties on Sunday as the main disturbance moves slightly to
the east.

The Weather Prediction Center currently has all of Deep South Texas
in a Slight Risk (level 2 of 4) for excessive rainfall on Saturday,
and the Coastal Counties under a Marginal Risk (level 1 of 4) for
Sunday.  Current probabilistic guidance for Saturday indicates a 15
to 25% risk that rainfall could exceed flash flood guidance.  While
areas further north (closer to Corpus and Houston) are expected to
receive the heaviest rainfall, given these probabilities, it is
therefore possible that Saturday's excessive rainfall risk could
trend upward if guidance can agree better on where the areas of
heaviest precipitation will occur, or if the heaviest expected rainfall
trends more southward.

Most of the rain received this weekend is expected to be beneficial.
It is most likely that the majority of areas will receive between
0.5-1.5 inches between now and Monday morning. However, it is
possible that some localized areas could receive up to 6 inches
where locally heavy rainfall occurs. Areas that will be prone to
isolated flash flooding are places where an excess of rain falls
over a short period of time (2- 3 inches an hour), or if training
showers and storms happen to form, with several showers going over
a single area in succession. Right now, the highest precip totals
and therefore highest chances of excessive rainfall are expected
over the eastern portion of the Northern Ranchlands. However,
isolated to scattered flash flooding could still happen anywhere
in Deep South Texas and it would be difficult to pinpoint
precisely where isolated flash flooding will occur, as shower
development will be scattered and random. Therefore, all flood-
prone areas should be prepared for the possibility this weekend,
despite most areas only expected to actually receive beneficial
rain.

Low rain chances continue into Monday as the atmosphere remains
somewhat disturbed, with the main chances (20-30%) in the Western
Ranchlands as more Sierra Madre convection is expected to form.
Conditions dry out Tuesday, but moderate rain chances (30-60%)
return for Wednesday and linger (20-30%) for Thursday before
becoming dry again for next weekend. Temperatures will remain warm
and humid through the next week, with Mild (level 1 of 4) and
Moderate (level 2 of 4) Heat Risks throughout the week.

In addition, a moderate risk of life-threatening rip currents are
expected to impact area beaches through at least Saturday
afternoon.

&&

.AVIATION...
(18Z TAFS)
Issued at 1248 PM CDT Fri May 22 2026

VFR conditions are expected at all airports with light to moderate
southeasterly winds.  Overcast conditions are expected to develop
this evening, and there is a small possibility that MVFR conditions
could briefly develop tonight, but confidence was not high enough to
include it in the TAF product.

&&

.MARINE...
Issued at 1248 PM CDT Fri May 22 2026

Favorable conditions are expected this weekend into next week with
light to moderate southeasterly winds and low (2 to 4 feet) wave
heights.  Conditions could briefly deteriorate in the immediate
vicinity of any showers and thunderstorms that form offshore,
particularly over the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             79  91  77  90 /  10  50  60  70
HARLINGEN               76  90  74  90 /  10  60  70  70
MCALLEN                 77  91  75  91 /  20  70  70  50
RIO GRANDE CITY         75  90  73  91 /  30  50  60  30
SOUTH PADRE ISLAND      80  85  79  84 /  20  40  60  60
BAYVIEW/PORT ISABEL     78  89  76  89 /  10  50  60  70

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Flood Watch through Monday morning for TXZ248>255-351-353>355-
     451-454-455.

GM...None.
&&

SHORT TERM...55-MM
LONG TERM....55-MM
AVIATION...55-MM