314
FXUS64 KBRO 180225
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
925 PM CDT Tue Jun 17 2025

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

.KEY MESSAGES...
Updated at 915 PM CDT Tue Jun 17 2025

* Hot, humid, and at times breezy conditions are expected to persist
  through Thursday with Moderate (Level 2 of 4) Heat Risk.

* Beginning on Thursday and possibly persisting through early next
  week, there will be day-to-day chances for showers and storms,
  amid a large-scale pattern shift.

* Axis of heaviest rainfall has shifted south over east-northeastern
  Mexico; best chance for rain here will be over the Lower Valley.

* Temperatures will be slightly cooler due to the increased cloud
  and tropical sourced rain chances.

* Any rain that falls will have the chance to be heavy; continue to
  monitor the latest forecast for any changes/updates.

* Outside of any showers/thunderstorms, marine conditions will
  generally be favorable through early next week.

&&

.SHORT TERM...
(Tonight through Thursday night)
Issued at 915 PM CDT Tue Jun 17 2025

Ahead of an impending significant large-scale weather pattern change
that`s expected to take place late this week into next week across
the CONUS, much of the same type of weather of recent is expected to
continue across Deep South Texas and the Rio Grande Valley through
much the short term period. That being hot, humid, mainly rain-free,
and at times breezy weather with moderate (Level 2 of 4) Heat Risk
through Wednesday night.

There are two features, specifically, that will be driving our
weather through Thursday: 1) a broad 1020-1025 hpa sfc high
pressure system parked over the western Atlantic Ocean, just off
the SE U.S. Coast, and 2) a 591 dam ridge or "heat dome". Being
located on the western edge of the first feature, south-southeast
winds will continue through Thursday. These winds could become
breezy at times with winds gusting as high as 25-40 mph,
especially on Wednesday, as the sfc pressure gradient tightens at
times in response to a nearby weak trough over the Sierra Madre.
Additionally, these winds will continue to support moist and warm
air advection (WAA) over the region through the short term
period. Subsidence from the the second feature (the 591 dam heat
ridge) will help to keep the area rain-free or mostly rain-free
through Wednesday night.

That said, tonight and Wednesday night will continue to be very
warm, humid, and at times breezy under mostly clear to partly
cloudy skies. Wednesday will feature another hot day with a
Moderate (level 2 of 4) Heat Risk. Daytime readings are expected
to top out in the mid 90s to lower 100s across the area, with the
exception of mid 80s to lower 90s along/near the Lower Texas Coast
and South Padre Island.

Thursday will be similar to Wednesday as far as the airmass.
However, clouds and the chances for showers and storms will begin to
increase in response to the aforementioned heat ridge breaking
down/weakening over the region and shifting northeast towards the
eastern 2/3rds of the country. The first of a series of tropical
waves (tropical upper tropospheric troughs, or TUTTs) will begin to
move into the the region from east to west on the southwestern edge
of the departing ridge.

Over the past 24 to 48 hours, there has been a southward shift in
the placement of the heaviest rainfall and these tropical waves,
with that being over east-northeastern Mexico. That said, shower
and thunderstorm chances remain on the table during the day on
Thursday given the close proximity to east-northeastern Mexico.
Elevated precipitable water (PWAT) values will foster efficient
tropical-type rains should any rain fall over parts of Deep South
Texas and the Rio Grande Valley on Thursday.

In the hours ahead, we will continue to fine tune the forecast, so
stay tuned for further updates. Currently, we have 20-40% chances
for rainfall on Thursday along and west of IH-69C. Along and east of
IH-69C, the probabilities increase to categorical 50-60% with the
highest confidence placed over the Lower Rio Grande Valley. After a
stretch of hot and dry weather, the rain potential on Thursday will
be welcomed across much of the region.

&&

.LONG TERM...
(Friday through next Wednesday)
Issued at 915 PM CDT Tue Jun 17 2025

As alluded to in the short term discussion, the long term forecast
period will consist of a significant weather pattern change across
the CONUS, that will include the first significant heat wave of the
season for folk across the Midwest, Northeast, and Mid-Atlantic.
This large-scale change to the weather pattern nationally will
result in quite a change here across Deep South Texas as the
pattern becomes increasingly unsettled (wet/stormy) and not as hot
due to the increase in clouds and rain chances.

On a deep southeasterly flow aloft regime, several global computer
models/ensembles continue to advertise a series of tropical sourced
rains from tropical waves or TUTTs tracking towards and at times
over parts of Deep South Texas Thursday night through the early
parts of next week. Most of these waves are expected to track to
our south across east-northeastern Mexico. As a result, most of
the rainfall production is expected to also fall across east-
northeastern Mexico. It`s worth noting that with longer range
model guidances, the average model error beyond three days is over
150 miles. That said, these waves will be close enough in
proximity yield day-to-day chances for showers and thunderstorms
through the extended.

Most of the convection is expected to be diurnally driven,
coinciding with max daytime heating. However, we, can`t rule out
rain through the nighttime, especially if one of the stronger
tropical waves track overhead during that time. Given the tropical
airmass/regime in place, elevated PWAT values will support
efficient tropical type rainfall any place that happens to receive
rainfall during this time period. Any slow moving or training of
storms over the same area could result in instances of
flooding/flash flooding. Given the synoptic setup as well as the
location and track of these tropical waves, the highest chances or
probabilities of rain/storms will be along and east of IH-69C,
especially over the Lower Valley (ie Cameron County). Again, at
this time, most of the rain has shifted southward and is expected
to fall over east-northeast Mexico.

We will continue to keep close watch on trends in the coming
days and update accordingly. For now, stay tuned to the latest
forecast at www.weather.gov/bro/, follow us on Facebook, Twitter,
or Slack/NWSChat 2.0. and if you need to, begin or continue to
clear out any clogged drainage (canals, culverts, ditches, etc.)
and have a flood safety plan in place.

Finally, temperature anomalies are expected to run near normal to
slightly cooler than normal through the balance of the period due
to the potential increase in cloud coverage and influx in
rain/thunderstorm chances. Daytime high temperatures each day are
progged to be in the lower to mid 90s. Meanwhile, nighttime lows
are forecasted to be in the 70s through the long term forecast
period.

&&

.AVIATION...
(00Z TAFS)
Issued at 626 PM CDT Tue Jun 17 2025

Through 00z Thursday....Though there could be a few MVFR clouds
around from time to time, flying conditions will remain VFR through
the 00z TAF period.

Winds will continue out of the southeast 10-20 kts with gusts as
high as 30 kts, through the TAF period.

&&

.MARINE...
Issued at 915 PM CDT Tue Jun 17 2025

Generally favorable marine conditions will prevail through the
weekend and into early next week with low to moderate seas and light
to moderate southeast winds. A locally enhanced pressure gradient
may result in periods of Small Craft Exercise Caution conditions
during the afternoon hours along the Laguna Madre and nearshore Gulf
waters through the end of the week. Otherwise, there is a medium to
high chance (40-80%) of showers and thunderstorms beginning Thursday
and continuing through early next week. Locally enhanced winds and
seas are likely within any showers and thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             94  81  94  80 /   0   0  10  20
HARLINGEN               97  78  96  78 /   0   0   0  10
MCALLEN                101  79 100  80 /   0   0   0   0
RIO GRANDE CITY        100  77  99  78 /   0   0   0   0
SOUTH PADRE ISLAND      88  81  88  81 /   0   0  10  20
BAYVIEW/PORT ISABEL     93  79  93  80 /   0   0  10  10

&&

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

$$

SHORT TERM...23-Evbuoma
LONG TERM....23-Evbuoma
AVIATION...23-Evbuoma