554
FXUS64 KBRO 142332 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
632 PM CDT Fri Jun 14 2024

...New AVIATION...

.SHORT TERM...
(Tonight through Saturday night)
Issued at 316 PM CDT Fri Jun 14 2024

Atmosphere does not change much between today and Saturday night
with Deep South Texas in between a mid-level ridge over NW Mexico
and over the South/SE States. A weak inverted trough is noted over
the Central and Southern Gulf extending over the Yucatan
Peninsula of Mexico and a shortwave trough is expected to pass
east across the Central Plains Saturday. Atmospheric moisture
remains limited in the lower 800mb with very dry air aloft. Any
showers or thunderstorms will be very isolated along the daily
afternoon sea breeze with all deterministic models indicating pops
only in the 5-15 percent range. At this time with low confidence
and the low guidance will keep pops at silent 10 percent.

This leaves us with the heat with no real changes in this element
either. Above normal highs are once again forecast with the NBM
continuing to be under achieving recent maximums. Have bumped up the
highs for Saturday a few degrees to accommodate this shortfall. Heat
indices Saturday afternoon to range from 105-110 degrees with an
hour or two of 112 degrees in a few spots. Overnight lows continue
to elevated with persistence the best forecast here. Expect minimums
Saturday and Sunday morning to range from 75-80.

&&

.LONG TERM...
(Sunday through next Friday)
Issued at 316 PM CDT Fri Jun 14 2024

Key Messages:

* Confidence continues to increase on a potential tropical system
  over the Southwest Gulf of Mexico next week bringing Deep South
  Texas and the Rio Grande Valley beneficial, soaking rains next week

* National Hurricane Center (NHC) has medium (50%) chance for
  tropical development over the Southwest Gulf of Mexico over the
  next 7 days.

* Current forecast suggest 2-5 inches of rain could fall by Friday
  with locally higher amounts up to 7 inches.

* Rain are expected to come in waves in the form of showers and
  storms with the greatest concentration and rain amounts between
  Wednesday and Friday

* Adverse marine conditions are expected to develop next week
  (includes increased rip current, high surf, and coastal flood risk)

The long-term forecast period will continue to focus on the
increasing prospects of a much-needed, beneficial, soaking rainfall.
Global deterministic forecast models and ensembles have come into
better agreement from previous iterations for a tropical system to
develop over the Southwestern Gulf of Mexico (SWGOM) near the Bay on
Campeche around Tuesday of next week. This tropical system is then
forecast to shift west-northwest into eastern Mexico. Despite the
core of the tropical system being located well to our south,
forecast models/ensembles are indicating a plume of deep tropical
moisture advecting into the region through next week in the form of
multiple rounds of showers and thunderstorms. The highest
probabilities/confidence and rainfall/QPF amounts are expected to
occur between Wednesday and Friday. Currently, the National
Hurricane Center (NHC) has continues to monitor and has a medium
(50%) chance for tropical development over the southwestern parts of
the Gulf of Mexico over the next 7 days.

We open up the long-term period on Sunday which will be our driest
day of the new week and a day that will feature very warm to hot and
humid conditions under a mix of sun and clouds. Daytime highs are
expected to range between the upper 90s to lower 100s and heat
indices between 105-111F degrees. An isolated shower or thunderstorm
can`t be ruled out, particularly near the coast amid increased sfc
based differential heating during the afternoon hours. Monday-
Tuesday, precipitation chances and coverage of precipitation
increases from east to west as the tropical system becomes better
organized and deep tropical moisture associated with it continues to
advect into the region. Currently have 30-60% PoPs on Monday from
McAllen and points east with the highest probabilities over/along
the island. By Tuesday, those numbers and coverage increase a bit
more. Have 30-70% PoPs from Starr/Jim Hogg County to the coast with
the coastal areas having the highest probabilities. As highlighted
earlier, we expect for any showers and thunderstorms to come in
waves from the outer bands of the developing tropical system to our
south. Underneath a scorching 594-597 dam heat dome centered over
the eastern U.S., 500mb heights around 588 dam and 850 mb temps
sampled between 20-25C will still result in very warm to hot and
humid conditions continuing Monday and Tuesday. That said, daytime
highs both days will range from the mid 90s to lower 100s with heat
indices potentially stronger than on Sunday due to higher
humidity levels as heat indices are expected to be between 106-113F.

Wednesday through Friday, the meat of this tropical rainfall event
will take place. That`s where we`ll see a greater concentration and
occurrence of tropical downpours to take place. As mentioned, rain
will come in waves of showers and thunderstorms Wednesday through
Friday. We have categorical PoPs across the entire region through
much of this period (Wednesday through Friday). During this time
period, max precipitable water (PWAT) values were sampled and are
expected to range between 2-3 inches which is +2 to +3 STDEVs above
normal, according to the latest 12z guidances. Additionally, plenty
of moisture advection will be in place as the Integrated Water Vapor
Transport (IVT) anomalies are ranging between +1 to +3 STDEVs above
normal. That said, preliminary forecast amounts between 2-5 inches
can be expected across Deep South Texas and the Rio Grande Valley by
Friday afternoon with locally higher amounts up to 7 inches for
areas that see repeated instances of heavy downpours.

This rain couldn`t have come at a better time as the Falcon
Reservoir water levels are at critical levels and much of the area
is under a D0 (Abnormally Dry) to a D1 (Moderate Drought), according
to the latest report from the U.S. Drought Monitor. Year to date,
precipitation deficits for Brownsville, Harlingen, and McAllen are
as follows: -2.32", -1.63", and -1.08", respectively. If all is
realized, this should flip many of our ASOS/Climate sites from a
rain deficit to a surplus for the year, end the drought over the
region, and improve the water levels over our reservoirs.

Given the very dry antecedent conditions, RFC`s flash flood guidance
(FFGs) are high across the region with the 1 hour ranging between 3-
4 inches along the Rio Grande Valley and 5-8 inches over the
Northern Ranchlands, and the 3 hour FFGs ranging between 3-5 inches
over the Rio Grande Valley and 5-9 inches over the Northern
Ranchlands. Given that the rainfall expected is expected over a 3
day span, flash flooding is not expected at this time. That said,
given that we are in a floodplain, there could be areas of general
flooding over urban/poor drainage and low-lying flood prone areas
next week (particularly in the Wednesday through Friday timeframe).

All told, elevated seas are anticipated along the Lower Texas Coast
next week (please see the Marine section below). An elevated risk of
rip currents (Moderate or High), Coastal Flood products (Advisory or
Warning), and High Surf products (Advisory or Warning) will likely
be needed at the local beaches and/or over the Gulf Waters.

Given the amount of cloud coverage and rounds of showers and
thunderstorms, temperatures will be tempered Wednesday through
Friday with highs ranging between the upper 80s to mid 90s across
the region. Nights will be continued warm and muggy (though not as
warm as early in the period) with overnight lows in the mid to upper
70s.

&&

.AVIATION...
(00Z TAFS)
Issued at 625 PM CDT Fri Jun 14 2024

Mostly clear skies and moderate east winds prevail across Deep
South Texas early this evening. Easterly winds will remain light
overnight into Saturday morning with brief gustiness between
19-24Z as the sea breeze front moves inland. VFR conditions are
expected for the next 24 hours.

&&

.MARINE...
Issued at 316 PM CDT Fri Jun 14 2024

Tonight through Saturday night...Weak pressure gradient persist
through Saturday night with gentle to light easterly to southeast
flow. A slight sea with little to no swell is expected through
Saturday with a low swell arriving form the east Saturday night.
Isolated showers or thunderstorms are possible.

Sunday through Friday Night....Adverse marine conditions
(including high seas over the Gulf) are expected to develop next
week amid the developing tropical system. In addition to waves of
showers and thunderstorms, an elevated risk of rip currents
(Moderate or High), coastal flood products (Advisory or Warning),
High Surf products (Advisory or Warning) at the local beaches
and/or Gulf Waters will likely needed next week especially mid to
late week.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             80  98  80  96 /  10  10  10  40
HARLINGEN               76  98  75  97 /   0  10  10  30
MCALLEN                 78 101  78  99 /   0  10   0  20
RIO GRANDE CITY         78 103  77 100 /   0   0   0  10
SOUTH PADRE ISLAND      83  89  83  88 /  10  10  20  50
BAYVIEW/PORT ISABEL     80  94  80  93 /  10  10  10  40

&&

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

$$

SHORT TERM...59-GB
LONG TERM....23-Evbuoma
AVIATION...63-KC