-- Discussion containing changed information from previous version are highlighted. --
152
FXUS64 KBRO 231139 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
639 AM CDT Sun Jun 23 2024

...New AVIATION...

.SHORT TERM...
-- Changed Discussion --
(Today through Monday)
Issued at 246 AM CDT Sun Jun 23 2024

Key Messages:

*There is a 40% chance of tropical development over the
 southwestern Gulf of Mexico over the next 48 hours and beyond.

*Risk of minor coastal flooding and a high risk of rip currents
 continue as seas and tides remain elevated.

The tropical airmass associated with the previously discussed
broad area of low pressure in the southwestern Gulf of Mexico will
continue to hold its grip over Deep South Texas for the short
term. The National Hurricane Center (NHC)`s latest update (2:00 AM
[EDT]) indicates a 40% (medium) chance of development over the
next 48 hours, and beyond, noting that the center of low pressure,
roughly 150 miles ENE of Tampico, may develop into a tropical
depression as it tracks northwestward before making landfall
tonight along the northeastern Mexico coastline. NHC also
highlights the primary threat to Deep South Texas will be
localized flooding from additional heavy rainfall.

As we have seen already, this tropical airmass has brought
anomalously high precipitable water values (PWAT) of near 2.5
inches, which has aided in developing scattered to numerous bands
of light to moderate, heavy at times, rainfall. Throughout the
morning today, this pattern is expected to continue into the
afternoon and evening. The current Weather Prediction Center (WPC)
Excessive Rainfall Outlook for today and tomorrow continue to
include Deep South Texas within a marginal risk for flash flooding
as well as the Storm Prediction Center keeps a general outlook
for thunderstorms over the next 2 days. Over the next 48 hours, an
additional 0.25 to 1.0 inches of rain is possible, with local
higher amounts possible, particularly in areas where lingering
heavy rain develops. As a result of increased cloud coverage, high
temperatures today will range from mid 80s along the coast to
upper 80s inland.

Meanwhile, just to the north of our region, a high pressure will
slowly work its influence southward and bring a temporary break in
rain bands across the Ranchlands tonight as well as slowly reduce
PWAT values in general. However, as the moisture surrounding the
low pressure to our south moves closer, conditions will remain wet
across the RGV. Tomorrow, as drier air advances on the humid
airmass, more breaks in the clouded are expected, which will warm
daytime highs from the mid to upper 80s near the coast to lower
to mid 90s inland. As the final surge of moisture arrives into our
region and increases instability with differential daytime
heating, thunderstorms and moderate to heavy showers are possible
across most of the County Warning Area during the day.

As mentioned above, additional minor coastal flooding is possible
today and tomorrow as higher seas will continue to result in a
high risk of rip currents and higher water levels, of 1 to 2 feet,
during high tide. This could lead to more nuisance flooding
erosion of beach dunes.
-- End Changed Discussion --

&&

.LONG TERM...
(Monday night through Saturday)
Issued at 246 AM CDT Sun Jun 23 2024

Key Messages:

- Rain chances lower after Monday
- More sun, tropical moisture could challenge heat advisory
  criteria each afternoon
- A disturbance in the Southwest Gulf has a 40 percent tropical
  cyclone formation chance

The long term trend will be for rain chances to normalize to sea
breeze activity, along with slightly increasing temperatures.
Elevated relative humidity values and the return of a bit more sun
will pressure heat index values upward toward borderline heat
advisory criteria for a few hours each afternoon starting Tuesday.

Although the tropical disturbance over the Southwest Gulf should
move into Northeast Mexico tonight, rain chances will remain
robust through Monday. Beyond Monday, rain chances will decrease
but plenty of residual moisture will remain over deep South Texas
and the RGV the remainder of the week.

Part of the logic for the more restrained (drier) forecast for
the week will be mid-level ridging building north and west of the
region. By early to mid-week a ridge will shift west from the
lower Mississippi Valley to Texas and then to over the Southwest
United States. This ridge will provide increased subsidence and
perhaps more stability to local conditions. On the other hand, the
position of the ridge could leave the Gulf slightly more
vulnerable to potential tropical cyclone development, though
nothing specific is showing up with any certainty right now.

That said, Gulf weather will remain unsettled this week and the
elevated moisture over land will support a better chance of daily
sea breezes Tuesday through Saturday impacting mainly eastern
sections of the CWA. The above assumes that there is no tropical
activity beyond the demise of the current disturbance in the
Southwest Gulf. Temperatures will be seasonal (near normal) to
slightly above normal as the week progresses. After Monday, a
steady, light to moderate southeast wind will develop, becoming
slightly stronger after mid-week. Skies will be partly cloudy for
the most part, becoming occasionally mostly cloudy as morning low
clouds develop and transition to a sea breeze.

&&

.AVIATION...
-- Changed Discussion --
(12Z TAFS)
Issued at 626 AM CDT Sun Jun 23 2024

Conditions are expected to be primarily VFR to MVFR through the
period as bands of rain showers continue to move through the area.
Rain chances look to decrease near the end of the period. Terminals
may briefly drop to IFR as heavier showers pass. Light to
moderate winds are expected to shift from the northeast this
morning to the southeast by the end of the period.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Issued at 246 AM CDT Sun Jun 23 2024

Today through Monday...NHC currently predicts a 40% chance of the
broad area of low pressure in the southwestern Gulf of Mexico
developing into a system, perhaps a tropical depression, before
making landfall tonight along the northeastern Mexican coastline.
Already, moderate to fresh winds in the coastal waters have
elevated offshore (20-60 nm) Gulf Waters to around 8.5 feet
overnight and a Small Craft Advisory is in effect over the Gulf
(0-60 nm). Conditions may change, depending on further
intensification, however the current guidance suggests a gradual
improvement of seas over the 24 to 48 hours with conditions
approaching Exercise Caution criteria.

Monday night through Thursday night...Light to moderate southeast
winds and low to moderate seas. The weather will remain unsettled
with isolated to scattered showers and thunderstorms from time to
time. A disturbance in the Southwest Gulf of Mexico has a chance of
developing into a tropical cyclone through the forecast. The current
forecast does not reflect potential tropical cyclone impacts.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             89  79  91  80 /  80  40  50  10
HARLINGEN               88  76  91  76 /  70  20  50  10
MCALLEN                 88  78  93  78 /  90  30  50   0
RIO GRANDE CITY         87  77  91  77 /  80  30  50  10
SOUTH PADRE ISLAND      85  82  87  82 /  80  40  40  10
BAYVIEW/PORT ISABEL     87  79  87  79 /  80  30  50  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Coastal Flood Advisory until 7 PM CDT Monday for TXZ351-354-355-
     451-454-455.

     High Rip Current Risk through Monday evening for TXZ451-454-455.

GM...Small Craft Advisory until 1 PM CDT this afternoon for GMZ150-
     155-170-175.

&&

$$

SHORT TERM...60
LONG TERM....54
AVIATION...60-BE