128
FXUS64 KBRO 050523 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1223 AM CDT Fri Sep 5 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 1220 AM CDT Fri Sep 5 2025

* Hot and rain-free conditions with Moderate (Level 2 of 4) to
  Major (Level 3 of 4) Heat Risk will continue Friday.

* A more widespread wet/unsettled weather pattern returns over the
  weekend through at least the early parts of next week.
  Additional chances mid to late week.

* Medium to high (35-80%) confidence for showers and thunderstorms
  each day from Saturday through next week; highest confidence
  along and east of IH-69C.

* Preliminary rainfall amounts between Saturday and Wednesday of
  next week will range between 1-3 inches with locally higher
  amounts.

* Flash flooding is possible and a Marginal (Level 1 of 4) Risk
  for Excessive Rainfall remains in place for all of Deep South
  Texas Sunday-Sunday night.

&&

.DISCUSSION...
Issued at 1035 PM CDT Thu Sep 4 2025

HOT AND DRY CONDITIONS TO PERSIST THROUGH FRIDAY:

Hot and rain-free conditions will persist for one more day on
Friday. Adequate sfc based differential heating courtesy of an
abundance of sunshine will allow for temperatures to surge to hotter
than normal levels with daytime highs topping out once again in the
upper 90s near the coast to the lower 100s most other places.
Widespread Moderate too Major Heat Risk will take place with heat
indices ranging between 100-112F degrees, despite a drier airmass in
place.

MORE RAIN, LOCALLY HEAVY RETURNS OVER THE WEEKEND THROUGH AT LEAST EARLY
NEXT WEEK:

Focus will then shift towards a return to more widespread rain
chances this weekend through at least the early parts of next week.
Global weather forecast models/ensembles continue to depict an
increase in deep tropical moisture advecting into the region from
the Gulf and from the remnants of Hurricane Lorena beginning this
weekend. Multiple forecast models including the GFS/NAM continue to
suggest a plume of precipitable water (PWAT) values topping out
between 2-2.5 inches over the local forecast area Saturday into the
early part of next week. A weakening/stalling frontal boundary to
our north over central/southern Texas coupled with the anomalously
high PWAT values will set the stage for day-to-day shower and
thunderstorm chances from Saturday/Saturday night through at least
the early parts of next week. Note: September is typically our
wettest month of the year!

While there still remains some uncertainty and some of the more
salient details still needs to be ironed out, it still appears that
there is the potential for some appreciable and much needed rainfall
through at least the early parts of next week.

As far as confidence, things continue to increase and right now
there is a medium-high (30-70%) chance for showers and thunderstorms
developing on Saturday across much of Deep South Texas and the Rio
Grande Valley, with categorical chances (>54%) located along and
east of IH-69C. Those probabilities are in the 70-80% range over the
Gulf Waters on Saturday. Sunday through Monday, there is a medium-
high (60-80%) chance (widespread categorical) for showers and
thunderstorms across the entire region. Monday night through Friday,
medium-high (30-70%) chances are in place (generally) across Deep
South Texas and the Rio Grande Valley. The highest probabilities
or confidence will be confined over the mid RGV, the lower RGV,
areas along and east of IH-69C, and over the Gulf Waters. Coverage
and intensity of showers and storms for the most part will be
diurnally driven. However, there will be chances (though lower
than the daytime) for showers and thunderstorms to take place
through the evening/night each day. Motorists should expect for
both the morning and afternoon commutes to be impacted.

As far as rainfall amounts, the 50th percentile (most likely
scenario) from the latest NBM run continues to suggest that anywhere
from 1.00-3.00 inches of rainfall with locally higher amounts is
possible by Wednesday morning over the region with the highest
amounts favored over the mid to lower RGV. We`ll continue to keep
close watch on these trends in the hours and days ahead!

In addition to the respectable rainfall totals during this period,
flash flooding is possible given how efficient the rainfall will be
courtesy of the heightened atmospheric moisture content and the
potential for some of the storms to be slow movers likely training
over the same areas given the weak jet stream winds/dynamics aloft
in place. This despite how antecedently dry it`s been. Given the
situation, the Weather Prediction Center (WPC) has maintained a
Marginal (Level 1 of 4) Risk for Excessive Rainfall Sunday/Sunday
night over the entire area. Motorists should expect and prepare for
both the morning and afternoon commutes to be impacted each day
from Saturday through early next week.

TEMPERATURE TREND SATURDAY THROUGH NEXT FRIDAY:

Despite Saturday being the onset of this rain event, it is expected
to be the hottest day of the weekend and days to follow. Depending
on the precise timing of shower and thunderstorm development, high
temperatures will have the chance to climb into the upper 90s to
lower 100s. High humidity levels will result in heat indices ranging
between 105-113F degrees on Saturday (hotter than normal levels).
This will result in a continuation of Moderate (Level 2 of 4) to
Major (Level 3 of 4) Heat Risk on Saturday.

Sunday through next week, the combination of clouds and rain will
help to keep the heat away. Anomalies are expected to run normal to
slightly cooler than normal levels for early September standards.
High temperatures during this time period will range in the lower to
mid 90s.

&&

.AVIATION...
(06Z TAFS)
Issued at 1220 AM CDT Fri Sep 5 2025

VFR conditions and southeasterly flow to prevail for the 06Z
cycle. Moderate winds and gusts around 20-25 kts return Friday
afternoon at all sites.

&&

.MARINE...
Issued at 1035 PM CDT Thu Sep 4 2025

Favorable marine conditions will continue with low to moderate seas
and light winds through Friday. The threat for showers and
thunderstorms increase over the weekend through at least the early
parts of next week as moisture increases and a cold frontal boundary
stalls to the north.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             96  80  95  80 /  10  20  70  50
HARLINGEN               99  77  97  75 /  10  10  70  30
MCALLEN                103  80 101  80 /   0   0  50  30
RIO GRANDE CITY        103  79 102  78 /   0   0  30  30
SOUTH PADRE ISLAND      90  83  90  82 /  10  40  70  60
BAYVIEW/PORT ISABEL     95  80  94  78 /  10  20  70  50

&&

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

$$

SHORT TERM...23
LONG TERM....23
AVIATION...69-HK