093
FXUS64 KBRO 182035
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
335 PM CDT Sat May 18 2024

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

...Oppressive Heat is the Story through Memorial Day Weekend...
...May 2024 Likely to be the Hottest on Record for Most of the
Valley...

.SHORT TERM...
(Tonight through Sunday night)
Issued at 335 PM CDT Sat May 18 2024

A weak quasi-stationary front situated just south of the CWA will
continue to undergo frontolysis as the airmass warms north of the
front and as winds continue to diverge and veer behind the front.
Otherwise, northwest flow aloft and mid/upper level ridging will
continue to build into the CWA through the short-term forecast
period.  The net result will be increasing subsidence and drying of
the tropospheric column.  This in turn will lead to rain-free
conditions and slightly warmer temperatures on Sunday.  Made a few
minor edits to the latest NBM temperatures but otherwise leaned in
that direction.  For now, we anticipate that heat advisory criteria
will not be met on Sunday.

The combination of very high surface-based moisture, drying aloft
and weak surface flow at night will lead to some fog development
tonight.  Still also expecting another round of stratus to develop
each night and persist into the morning hours given the very high
amount of boundary layer moisture.

Both the RAP-Smoke and GEOS-5 models depict the core of the haze and
smoke remaining across the open Gulf.  However, peripheral influx of
smoke and haze is still anticipated through the short-term period,
thus keeping the generally unhealthy air, especially for areas
generally east of I-69C.

&&

.LONG TERM...
(Monday through next Saturday)
Issued at 335 PM CDT Sat May 18 2024

Key Messages:
-Dangerous heat is the story through the week and into Memorial
 Day Weekend
-Fair to poor air quality to prevail until further notice for much
 of the RGV

A broad and very strong (for late May) 500 mb ridge will set up
camp in northern Mexico...stretching from Durango/Zacatecas
through the RGV region and centered from Durango through southern
Coahuila/Nuevo Leon to central Tamaulipas. This is similar to our
typical summer "La Canicula" pattern...only displaced a bit south
into Mexico which, in a sense, is even worse...as continued energy
waves moving through the central/southern Plains draw a continue
tap of moisture on southerly/southeasterly flow in the lower
levels that taps the eastern tropical Pacific, western Caribbean,
and southwest Gulf. With the ridge settled in and all of the
energy well to the north, rain chances will be virtually nil.

As for temperatures...the amazing statistic is not just the
persistent of triple-digit afternoon heat and "feels like"
temperatures to or above heat advisory (111 to 115 degrees) across
the populated RGV each day, but the persistent of oppressive
overnight temperatures in the 80s...only reaching the upper 70s
just before daybreak and only across rural areas. "Feels like"
temperatures will remain in the 90s all night in urban/suburban
Valley locations and other areas along/near the Rio Grande...which
adds up to accumulated heat impacts especially on those with
limited cooling both day and night. When comparing with 2023, the
expected conditions are matched will with mid to late *June* - a
month that was near all-time records.

Compounding the temperatures is a continuation of "ugly" air - a
result of increased agricultural burning in southeast
Mexico/Yucatan and Central American wildfires all being driven
north/northwestward on the persistent south/southeast flow but
also picking up higher dewpoint air from top 5 percentile warm sea
surface temperatures in the areas mentioned above. Overnight
inversions trap the moisture with the smoke...leading to higher
concentrations of condensation nuclei and hence air quality that
edges into the Unhealthy for Sensitive Groups and Unhealth (red)
range. Each day through the long term will likely have this
category...which is making spring 2024 one for the record books in
terms of numbers of days with USG (orange) and Unhealthy (red)
conditions.

Bottom lines? Follow heat safety guidelines, and if susceptible to
the dirty air, wear an N95 particulate-blocking mask and ensure
indoor air is truly "conditioned" through clean ducts, filters,
and unblocked circulation.

At the beach, moderate mainly south to north longshore currents
will greet swimmers enjoying the low 80s surf.

&&

.AVIATION...
(18Z TAFS)
Issued at 1223 PM CDT Sat May 18 2024

MVFR ceilings will slowly transition to VFR ceilings through this
afternoon across most of the RGV. The cumulus will be the most
enhanced across the KHRL and KBRO TAF sites this afternoon. MVFR
ceilings will again redevelop by 03-04Z this evening given the
very moist boundary layer flow aided by easterly flow. IFR
ceilings and MVFR visibilities will be possible after midnight
through 14Z Sunday. Slow improvement in vsbys/ceilings can be
expected after 14-15Z Sunday as daytime mixing develops.

&&

.MARINE...
Issued at 335 PM CDT Sat May 18 2024

Tonight through Sunday night...Modest 3-4 foot seas will generally
persist through the short-term period as the overall gradient will
remain in the weak to moderate range. These modest seas and 7-8
second period waves will generally maintain a moderate risk of rip
currents through the short-term period.

Monday through Thursday Night...Same stuff, different day:
Persistent south-southeast flow and enough gradient exists for
periodic Small Craft Exercise Caution conditions (15 to 20 knots
and gusty) each afternoon on Laguna Madre and overnight on the
open Gulf. Marine layer still holds, even though temperatures are
higher on the Gulf due to the heat. There`s still a ~20 degree
afternoon difference between sea and land so expect speeds closer
to 15 knots during the day on the Gulf. Seas will be a bit
difficult for small craft with a not-so-great combo of wind waves
and swell adding up to values in the 4-6 foot range.

&&

.CLIMATE...
Issued at 335 PM CDT Sat May 18 2024

How hot, you may ask? Let`s do the numbers (degrees Fahrenheit):
For May 2024 so far (day and night combined)...

Location(since)    Current Record(rank)   Prior record(year)

Brownsville(1878)       85.6 (1)               84.4 (2003)
Harlingen/Valley(1953)  84.1 (4)               85.6 (2003)
McAllen(1942)           86.9 (2)               87.1 (2009)
Rio Grande City(1897)   86.2 (3)               87.6 (2003)
Raymondville(1913)      85.3 (2)               85.4 (2003)
Port Mansfield(1958)    83.3 (1)               82.0 (2003)
Weslaco(1914)           84.8 (2)               85.7 (1933)

For the year so far:

Brownsville(1878)       72.5 (3)               73.5 (2020)
Harlingen/Valley(1953)  70.3 (6)               72.7 (2000)
McAllen(1942)           72.5 (5)               74.2 (2020)
Rio Grande City(1897)   70.5 (6)               73.3 (2000)
Raymondville(1913)      70.3 (6)*              72.0 (2020)
Port Mansfield(1958)    69.3.(3)               71.1 (2000)
Weslaco(1914)           70.2.(5)               72.8 (2000)

Given the aforementioned forecast through Memorial Day Weekend,
and no changes apparent beyond, May 2024 is a virtual lock for the
all-time record, with Brownsville likely to land more than 2
degrees above the prior record! The same prolonged stretch will
pull the annual rankings into the top five at all locations, with
some potentially reaching number 1.

And a searing June is expected to follow.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             79  94  79  96 /   0   0   0   0
HARLINGEN               75  96  75  98 /   0   0   0   0
MCALLEN                 77  99  78 100 /   0   0   0   0
RIO GRANDE CITY         77  98  76 101 /   0   0   0   0
SOUTH PADRE ISLAND      80  84  80  85 /   0   0   0   0
BAYVIEW/PORT ISABEL     77  89  77  95 /   0   0   0   0

&&

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

$$

SHORT TERM...80-MB
LONG TERM....52-Goldsmith
AVIATION...80-MB