Severe Thunderstorm Warning 19, NWS Brownsville, TX

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
636 AM CDT Wed May 20 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 634 AM CDT Wed May 20 2026

Key Messages:

* Day-to-day or near day-to-day chances for showers and
  thunderstorms is expected through next weekend and possibly beyond
  amid a major shift in the weather pattern.

* Strong to severe thunderstorms along with heavy rainfall and
  localized flooding is possible through next weekend.

* There is a low-medium chance for showers and thunderstorms tonight
  into Wednesday morning; greatest chances over the Northern
  Ranchlands.

* The Storm Prediction Center (SPC) has all of Deep South Texas
  under a Marginal Risk (Level 1 of 5) for severe thunderstorms with
  the exception of northern Jim Hogg and Zapata counties which is
  under a Slight Risk (Level 2 of 5).

* The Weather Prediction Center (WPC) has our northwestern sections
  under a Marginal Risk (Level 1 of 4) for Excessive Rainfall
  Wednesday evening/night and all of Deep South Texas under a
  Marginal Risk for both Thursday and Saturday.

&&

.DISCUSSION...
Issued at 1042 PM CDT Tue May 19 2026

An increasingly active/wet weather pattern signifying a major
pattern change from dry to wet remains the primary weather concern
through the forecast period or through early next week.

Through tonight and into Wednesday morning, we're tracking trends
and the potential for showers and thunderstorms to develop as
ongoing convection over Central Texas propagates southward along an
outflow boundary. As of this update, there remains a low-medium (20-
60%) chance/confidence for showers and thunderstorms to develop and
impact our region. As far as timing, the estimated time of arrival
for storms is expected to be somewhere between the hours of 3-9
AM CDT Wednesday morning. One of the primary uncertainties is
whether or not the MCSs/complexes of storms upstream across
Central Texas will maintain it's momentum as it propagates
southward through tonight into Wednesday morning.

Some of the latest models favors a more eastward placement
suggesting that most of the activity will pass to our northeast
(i.e. Coastal areas of Corpus Christi) by Wednesday morning with
maybe some stratiform showers/isolated thunder developing along or
immediately behind the outflow boundary. Capping and the time of day
could also serve as limiting factors in the magnitude of storms,
especially further south along the Rio Grande Valley. That said, the
best chances are across the Rio Grande Plains and the Northern
Ranchlands tonight through Wednesday morning. The Storm Prediction
Center (SPC) has maintained a Marginal Risk for severe thunderstorms
though tonight into Wednesday morning for all of Deep South Texas
with the exception of northern Zapata and Jim Hogg Counties, which
are under a Slight Risk. A Marginal Risk for Excessive Rainfall
has been applied to northern Brooks, jim Hogg, and Zapata
counties. We'll continue to monitor trends through tonight and
update as necessary.

Wednesday through early next week, day-to-day or near day-to-day
rain chances is expected. Driving this active pattern is an active
southwest flow aloft sub-tropical jet in which multiple
impulses/shortwave energies tracking over the Sierra Madre, and a
nearby frontal boundary to our north.

Persistent southerly flow near the sfc will continue to pool in deep
tropical moisture helping to maintain high atmospheric water content
through early next week. This is justified with sample maximum
precipitable water (PWAT) values between 1.80-2.50 inches, some 1-3
STDEVs above normal and above the 90th percentile of sounding
climatology for mid to late May. Furthermore, high instability
values will be present through this week with steep mid level lapse
rates between 6.5-8.0 C/km, SBCAPE values between 2,000-4,000 J/kg,
MLCAPE values between 1,000-2,000 J/kg, a moderately to very
unstable atmosphere with Showalter values ranging between -2 and -6.

All in all, the combination of a favorable mid-upper level 500 mb
steering pattern, high atmospheric moisture content, and high
instability will support a noticeable change to a wetter/active
weather pattern through the remainder of this week and possibly
beyond. The best chances for rain this week looks to be on Thursday
and then again over the weekend (i.e. Friday night through Sunday).
Wednesday evening/night, 30-50% PoPs exist primarily along and west
of IH-69C/US-281. Thursday-Thursday night, 30-60% chances exists
with widespread categorical chances (50-60%) for showers and
thunderstorms exists during the day on Thursday, and over the
Northern Ranchlands and areas along and west of IH-69C/US-281.
Meanwhile, 30-50% chances exists over the mid-lower Rio Grande
Valley on Thursday. Friday night through Sunday, PoPs range
between 40-70%. Additional chances (to a lower extent; between
20-50%) exists through early next week. Strong to severe
thunderstorms are possible given the atmospheric and forcing
ingredients highlighted above.

However, heavy rainfall will be the primary threat. Given the high
atmospheric moisture content available, heavy rainfall and instances
of flooding is possible through next weekend. This is especially
true for slow moving thunderstorms that repeatedly track over the
same areas. The Weather Prediction Center (WPC) has our northwestern
section (i.e. Zapata, Jim Hogg, Starr, and northwestern Brooks)
under a Marginal Risk (Level 1 of 4) for Excessive Rainfall for
Wednesday Night and all of Deep South Texas under a Marginal Risk
(Level 1 of 4) for Excessive Rainfall for both Thursday and Saturday.

Through Saturday, quantitative precipitation forecasts (QPF) or
rainfall amounts are still expected to range between 1-2 inches with
locally higher amounts across Deep South Texas and the Rio Grande
Valley. The rain to come will certainly prove to be beneficial,
helping to further improve the D1 (Moderate) to D2 (Severe) Drought
status across the region.

Temperature-wise, the combination of the heat ridge relaxing and
day-to-day storm chances will allow for temperatures to run near
normal levels for late May. Through early next week, high
temperatures will generally range between the upper 80s to lower
90s. Overnight lows will run slightly above normal with readings
mainly in the 70s (lower 80s Cameron County and over SPI).

&&

.AVIATION...
(12Z TAFS)
Issued at 634 AM CDT Wed May 20 2026

A TEMPO has been included in the TAFs due to the steady
progression of a squall line of showers and thunderstorms from
the north. Otherwise, MVFR to VFR will prevail through the next
24 hours.

&&

.MARINE...
Issued at 1042 PM CDT Tue May 19 2026

Adverse (Small Craft Exercise Caution) conditions will persist
through Thursday evening. Friday through early next week, moderate
seas along with light to moderate winds are expected. Daily or near
daily shower and thunderstorm chances will be around through the
forecast period.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             91  79  90  79 /  20  10  50  20
HARLINGEN               92  76  90  75 /  20  20  50  30
MCALLEN                 93  77  91  77 /  20  30  50  50
RIO GRANDE CITY         94  74  90  74 /  40  50  60  40
SOUTH PADRE ISLAND      85  80  85  81 /  20  10  40  20
BAYVIEW/PORT ISABEL     90  78  89  78 /  20  10  50  20

&&

.BRO WATCHES/WARNINGS/ADVISORIES...None.

&&

Special Weather Statement
National Weather Service Brownsville TX
520 AM CDT Wed May 20 2026

TXZ249>252-353-201100-
Brooks TX-Jim Hogg TX-Northern Hidalgo TX-Starr TX-Inland Kenedy TX-
520 AM CDT Wed May 20 2026

...STRONG THUNDERSTORMS WILL IMPACT SOUTHWESTERN KENEDY...
SOUTHEASTERN JIM HOGG...NORTH CENTRAL HIDALGO...NORTHEASTERN STARR
AND BROOKS COUNTIES THROUGH 600 AM CDT...

At 520 AM CDT, Doppler radar was tracking a cluster of strong
thunderstorms over Rachal, moving southeast at 40 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Agua Nueva, Encino, Rachal, Puerto Rico, La Reforma, El Coyote Ranch
Airport, San Isidro, San Rafael Ranch Airport, Santa Elena, and
Delmita.

This includes US Highway 281 between mile markers 714 and 752.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 2700 9869 2720 9815 2674 9782 2653 9835
TIME...MOT...LOC 1020Z 322DEG 36KT 2687 9815

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

Caceres

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Special Weather Statement
National Weather Service Brownsville TX
644 AM CDT Wed May 20 2026

TXZ253>255-353-201230-
Inland Willacy TX-Southern Hidalgo TX-Northern Hidalgo TX-
Inland Cameron TX-
644 AM CDT Wed May 20 2026

...STRONG THUNDERSTORMS WILL IMPACT SOUTHEASTERN HIDALGO...
NORTHWESTERN CAMERON AND WESTERN WILLACY COUNTIES THROUGH 730 AM
CDT...

At 644 AM CDT, Doppler radar was tracking a cluster of strong
thunderstorms over Monte Alto, or near La Villa, moving south at 25
mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Harlingen, Weslaco, Mercedes, Raymondville, La Feria, Elsa, Edcouch,
Santa Rosa, Lyford, and La Villa.

This includes the following highways...
 Interstate Highway 69 E between mile markers 26 and 51.
 US Highway 77 between mile markers 758 and 762.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 2654 9813 2660 9781 2660 9775 2620 9761
      2612 9799
TIME...MOT...LOC 1144Z 339DEG 21KT 2636 9793

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

Caceres

Special Weather Statement
National Weather Service Brownsville TX
715 AM CDT Wed May 20 2026

TXZ253-255-201300-
Southern Hidalgo TX-Inland Cameron TX-
715 AM CDT Wed May 20 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN HIDALGO AND
SOUTHWESTERN CAMERON COUNTIES THROUGH 800 AM CDT...

At 715 AM CDT, Doppler radar was tracking a strong thunderstorm over
La Feria Public Library, or near La Feria, moving south at 40 mph.

HAZARD...Wind gusts up to 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Harlingen, San Benito, Mercedes, La Feria, Progreso, Los Indios,
Santa Maria, La Paloma, Rangerville, and Brownsville.

This includes the following highways...
 Interstate Highway 69 E between mile markers 18 and 26.
 US Highway 281 between mile markers 804 and 832.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 2599 9763 2600 9762 2601 9765 2603 9764
      2603 9769 2602 9769 2604 9771 2602 9774
      2605 9777 2603 9779 2606 9780 2605 9786
      2607 9786 2606 9787 2607 9793 2605 9794
      2606 9801 2614 9800 2620 9761 2596 9759
TIME...MOT...LOC 1215Z 003DEG 33KT 2611 9781

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

64-Katz