412
FXUS64 KBRO 131931
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
231 PM CDT Thu Jun 13 2024

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

.SHORT TERM...
(Tonight through Friday night)
Issued at 151 PM CDT Thu Jun 13 2024

500mb high pressure axis along the New Mexico/West Texas border
pivots eastward through Friday taking on an east to west
orientation. Modest 1000-700mb layer moisture (55-75%) today
lowers slightly Friday (55-65%) as subsidence from the passing
center of the ridge squashes the limited available moisture below
700mb. The overall moisture content in form of precipitable water
is shown to lower from 1.90 inches observed on the Thursday 12Z
Brownsville sounding to a GFS forecast of 1.6 inches Friday.

Satellite loops show a nice cumulus band along the sea breeze
pushing inland with isolated showers noted over northern Kenedy,
over Cameron County and south of the Rio Grande over Tamaulipas,
Mexico as of 130 PM LT. Until sunset or shortly after, there
remains a slight chance of showers or a thunderstorm west of I-69E
as the sea breeze front traverses westward across the RGV/Deep
South Texas. Thereafter, mostly clear and calm with mild to warm
overnight temperatures of 75-80 degrees. Friday mostly sunny with
a very low chance (10%) of a sea breeze shower with highs climbing
well into the 90s to lower 100s. Local beaches will see highs
reach the upper 80s. Another sultry night to start the weekend
with lows only dipping into the 75-80 degree range.

&&

.LONG TERM...
(Saturday through next Thursday)
Issued at 151 PM CDT Thu Jun 13 2024

Key message - We are watching the Bay of Campeche/Southwest Gulf for
potential tropical development.

While chances have increased for tropical development to the
south (Southwest Gulf) over the next few days, any potential
system is likely (at this writing) to ultimately move into Mexico,
due in part to broad mid-level ridging holding sway over Texas
and dissuading the northward movement of lower latitude systems.
For reference, the NHC gives the chance for cyclone development as
40% for late this weekend or early next week. Regardless of the
final outcome to the south, tropical moisture will be able to
surge north, and local rain chances are forecast to trend upward,
especially for Tuesday through Thursday.

Saturday through Monday will feature afternoon sea breeze
activity, with rain chances spreading a bit farther inland each
day. On Saturday, a 700 mb inverted trough/tropical wave shows up
in the models over the Southwest Gulf, deepening to 500 mb by
Sunday. This trough will remain in place into the early part of
next week. As mid-level ridging drops anchor and builds over the
Southeast United States/Mid-Atlantic region, it will open up a
path for tropical moisture to move north along the Northeast
Mexican coastline toward the lower Texas coast.

By Wednesday and Thursday, global models support the chance to
likely categories of rain percentages. In terms of amounts, NBM
deterministic numbers suggest that over an inch of rain can be
expected for the lower Valley on both Thursday and Friday. More
aggressive numbers, reflecting copious moisture and high rain
producing efficiency, could start us out at an inch as early as
Saturday, ramping up to around three inches for the 24 hours from
Wednesday to Thursday. For the week, those worst case scenario
numbers could support up to ten inches of rain for the lower
Valley spread across the work week, but focused mainly from
Tuesday through Friday. The Ranchlands and Mid-Valley worst case
scenario rain accumulation amounts are on par with the lower
Valley since potential rain bands will affect the entire CWA.
Something to watch for in later forecasts, however, will be that
if a potential system strengthens, it could actually start to
impact rain chances downward, as some tropical moisture would be
pulled closer to the storm, causing the heavier rainbands to
remain farther south. However, since this tropical cyclone has yet
to develop, the current thought process is to go with a more
widespread (generous) rainfall scenario.

The generally welcome rainfall will not be the only thing to
impact the CWA over the course of the long term forecast. Because
of an enhanced pressure gradient, stronger east to southeast flow
will develop, generating larger swells that may lead to a higher
rip current risk along the beaches, and even beach runup and
coastal flooding concerns next week.

As for temperatures in the long term, highs will start off in the
range of upper 90s for most of Deep South Texas and the Rio
Grande Valley, with a few areas in the triple digits, but will
taper off by Wednesday to being mostly in the 90s, thanks to
extra cloud cover and increased rain chances. Heat index values
will continue in the 105 to 110 degree range through Tuesday, but
will be lower, 102 to 107 degrees Wednesday and 95 to 105 degrees
on Thursday, mid week. Low temperatures will be mostly in the
70s, but a few places could bottom out near 80.

&&

.AVIATION...
(18Z TAFS)
Issued at 1226 PM CDT Thu Jun 13 2024

As high pressure remains nearby VFR conditions with light east to
southeast winds persist through the next 24 hours. A very low
probability (10%) of a shower or rouge thunderstorm is possible
but should be brief with minor impacts.

&&

.MARINE...
Issued at 151 PM CDT Thu Jun 13 2024

Tonight through Friday night...Models continue to show a weak
pressure gradient persisting over the western Gulf of Mexico
tonight, Friday and Friday night. Gentle to light south winds
today back southeast to east Friday as upper level high pressure
shifts eastward. Seas remain nearly flat with buoy 42019 reporting
seas at 1 foot as of 1 PM today. Isolated showers and/or
thunderstorm being observed offshore have a low probability
reaching the Laguna Madre this today over this evening. Low
probability continues for Friday for all coastal waters.

Saturday through Tuesday night...Moderate east to southeast winds
and moderate seas will slowly transition higher into the weekend.
The weekend will feature moderate to fresh east to southeast winds
and building seas. Gulf wave heights will approach small craft
advisory criteria late in the weekend for the offshore waters, and
may also reach small craft advisory criteria for the nearshore
waters by early next week. Marine weather will remain unsettled,
with isolated to scattered showers and thunderstorms possible
through the long term.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             78  97  80  96 /  10  20  10  40
HARLINGEN               74  99  75  97 /   0  20  10  40
MCALLEN                 78 100  78  98 /   0  10   0  20
RIO GRANDE CITY         78 100  77  98 /  10  10   0  10
SOUTH PADRE ISLAND      82  89  83  88 /   0  20  20  50
BAYVIEW/PORT ISABEL     78  93  79  93 /  10  20  10  40

&&

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

$$

SHORT TERM...59-GB
LONG TERM....54-BHM
AVIATION...59-GB