Severe Thunderstorm Warning 57, NWS Brownsville, TX

Area Forecast Discussion
National Weather Service Brownsville TX
122 PM CDT Thu May 8 2025

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

.SHORT TERM...
(Now through Friday night)
Issued at 122 PM CDT Thu May 8 2025

Key Messages:

- There is a medium to high chance (30-60%) of isolated pockets of
  3-5 inches of rain across portions of the region, which may
  result in an increased threat for flash flooding.

- Strong to severe thunderstorms through the late afternoon hours
  and overnight with a primary threat of damaging wind gusts and
  large hail.

An active short term period is expected through early Friday
morning across Deep South Texas and the Gulf waters with strong to
severe thunderstorms capable of producing damaging wind gusts,
large hail, and heavy rainfall. The latest suite of high resolution
and probabilistic guidance indicate there is a potential for
isolated 3-5 inches of rainfall through early Friday morning given
the very rich moisture content across Deep South Texas, mainly
along and east of US-281. The HREF 24-hour probability-matched
mean also highlights a swatch of localized 3-5 inches through
Friday morning across portions of the Lower/Mid Rio Grande Valley
and the Northern Ranchlands.

For this afternoon and evening, there will be two areas of
convection that could pose a threat for severe weather. The first
area will be along a weak boundary draped across portions of the
Lower to Mid RGV, which will serve as a focus for convective
development through the afternoon hours. A favorable environment
characterized by high moisture content (PWATs of 2.15” observed
with this morning’s 12Z sounding), high instability (MUCAPE values
upwards of 3000 J/kg), and modest shear profiles (bulk shear
values upwards of 50 knots) would support a damaging wind gusts
and hail threat with any severe thunderstorms. However, this
morning’s activity may limit the severe potential somewhat. The
second area for convective development will be over the Sierra
Madre in Mexico late this afternoon and evening as a shortwave
approaches, with discrete cells quickly developing as it
encounters a highly favorable environment and translate east to
southeast. While initial development is expected to be discrete in
nature, upscale growth into an MCS or cluster of strong to severe
thunderstorms may develop and translate toward the region through
late this evening.

As the aforementioned shortwave approaches from Northern Mexico,
a line of showers and strong to severe thunderstorms is expected
to track across Deep South Texas from northwest to southeast late
this evening and overnight. With this activity, the main threats
are damaging wind gusts and heavy rainfall, although some large
hail cannot be ruled out over the Upper RGV and Northern
Ranchlands. Instances of flash flooding cannot be ruled out into
the overnight hours, especially over low-lying or flood-prone
areas.

Convection should exit the region by Friday morning, with only
some activity continuing through early Friday afternoon over the
Gulf waters. Otherwise, expect northerly winds to prevail through
tomorrow night and mostly sunny/clear skies. Expect lows in the
60s and highs in the 80s.

&&

.LONG TERM...
(Saturday through next Thursday)
Issued at 122 PM CDT Thu May 8 2025

In wake of the frontal passage, generally rain-free conditions and
near normal temperatures will prevail over Deep South Texas
through the weekend. Above normal temperatures are forecast for
most of the week next week with highs in the 90s region wide, and
portions of the Upper RGV and Northern Ranchlands realizing highs
of 100-101 degrees by mid week. In combination with the humidity,
this will result in a minor to moderate heat risk across Deep
South Texas.

&&

.AVIATION...
(18Z TAFS)
Issued at 1238 PM CDT Thu May 8 2025

A mix of IFR and MVFR conditions and variable winds prevail across
Deep South Texas early this afternoon. BRO radar currently
indicates scattered to numerous SHRA and TSRA across portions of
the RGV extending eastward along the coast/over the Gulf waters.
IFR to MVFR ceilings are expected through the majority of the TAF
period, though some brief periods of VFR ceilings are possible
this afternoon. Multiple rounds of convection are possible this
afternoon into tonight and will likely impact all three
aerodromes. Latest short-term model guidance continues to suggest
that scattered showers and thunderstorms will develop over the
area through the afternoon. There is increasing confidence that a
line of convection upstream will to move southeast through the
area tonight into early Friday morning.

&&

.MARINE...
Issued at 122 PM CDT Thu May 8 2025

Now through Friday night...Periods of showers and thunderstorms,
some severe, are expected through early Friday afternoon over the
Gulf waters ahead of the passage of a cold front. Locally enhanced
winds and seas are expected within any thunderstorms. East winds
will shift to the north and northeast late tonight into tomorrow
as the cold front tracks across the region. Small Craft Exercise
Caution conditions will be possible in wake of the frontal
passage, and low to moderate seas will prevail.

Saturday through next Thursday...Generally favorable marine
conditions will prevail with low to moderate seas and light to
moderate winds through early next week. A tightening pressure
gradient will result in increasing winds and seas by mid week, and
Small Craft Exercise Caution to Small Craft Advisory conditions
will return.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             71  83  65  83 /  80  40   0  10
HARLINGEN               68  84  63  85 /  70  30   0  10
MCALLEN                 71  86  67  87 /  80  30   0   0
RIO GRANDE CITY         69  85  65  84 /  90  20   0   0
SOUTH PADRE ISLAND      74  79  71  78 /  80  50   0  10
BAYVIEW/PORT ISABEL     71  81  66  82 /  70  40   0  10

&&

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

SHORT TERM...22-Garcia
LONG TERM....22-Garcia
AVIATION...63-KC

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