-- Discussion containing changed information from previous version are highlighted. --
397
FXUS64 KBRO 260542 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1242 AM CDT Sun May 26 2024

...New AVIATION...

.SHORT TERM...
(Tonight through Sunday night)
Issued at 105 PM CDT Sat May 25 2024

Key Messages:

* Excessive, Dangerous, Record-Breaking Heat Likely again on Sunday
* Triple digit highs expected for Brownsville, Harlingen, and
  McAllen on Sunday; Heat Indices will range between 115-130F
* Extreme risk of heat related impacts to anyone spending time
  outdoors and not taking the necessary precautions (per NWS
  HeatRisk Tool)
* High Risk for Rip Currents to continue through Sunday evening

Dangerous, excessive, record-breaking heat will continue to be
the story through the Memorial Day Holiday Weekend and/or through
the short term forecast period. Deterministic forecast
models/ensembles continue to advertise heat intensifying over the
local forecast area through Sunday as an anomalously strong sub-
tropical heat dome builds northward into the region (and so early
for this time of year). Tonight through Sunday, 1000-500 mb
thicknesses are expected to increase to between 588-590 dam, and
500 mb geopotential heights are expected to increase from 591 to
594 dam, which are both 2-3 STDEVs above normal.

After another hot day today, little relief is in store for
tonight. Aided by an increase in cloud coverage due to strong low
level moisture around and additional marine influences, much of
the warmth from today will be trapped underneath the cloud
coverage. That means little relief is in store as another very
warm and muggy night is expected. Overnight low temperatures will
challenge or even break standing records with values expected to
hold in the upper 70s to lower 80s (see Climate section below).
Another Heat Advisory is likely to be issued later this evening to
account for the very warm temperatures continuing through
tonight. With the low level jet (LLJ) increasing overnight, sfc
winds will be strong enough to keep any widespread mist/fog from
developing.

During the day on Sunday, forecast models indicate a 594 dam heat
dome building over the area. 850 temperatures were sampled
between 26-28C. This translates to sfc temperatures/daytime highs
ranging between 100-110F degrees across much of Deep South Texas
and the Rio Grande Valley (90s for the coastal areas). These
temperatures are hotter than normal for late May standards are
again are on the order of 2-3 STDEVs above normal. Furthermore,
these temperatures, if realized, will break previous records set
(see Climate section below). When you factor in the high dewpoint
values (in the mid to upper 70s), heat indices will be dangerously
hot ranging between 115- 130F degrees across much of Deep South
Texas and the Rio Grande Valley on Sunday. The worst of the heat
indices will be across Starr, Hidalgo, Inland Cameron, Inland
Willacy, Brooks, and Inland Kenedy Counties on Sunday. Another
Excessive Heat Warning will be issued later this evening for
Sunday.

A High Risk for Rip Currents will continue for the area beaches
along the Lower Texas Coast till 7 PM CDT on Sunday. Sunday night
will be similar to tonight with little to no relief expected as
overnight lows hold into the lower 80s. Winds will also be lighter
as well Sunday night.

All in all, this is a dangerous situation!

* Heat stroke is likely and death is possible to persons exposed to
  heat indices (real feel temperatures) of 116F or higher.
* Heat exhaustion is likely to persons unprepared for heat indices
  (feel like) temperatures between 111-120F degrees.
* Heat cramps and heat exhaustion are possible to persons not
  acclimated or unprepared for heat indices "feel like" temperatures
  near 120F.

&&

.LONG TERM...
(Monday through next Saturday)
Issued at 105 PM CDT Sat May 25 2024

There will be little relief from the frying pan heat heading into
the long term. Mid- to upper-level ridging anchored over Mexico
will provide strong subsidence across deep South Texas and the Rio
Grande Valley. Dangerous heat will persist through most of next
week with triple-digit temperatures for most inland locales. Due
to steady southeast surface flow, dew points poking into the 70s
will support elevated heat index values, which will encroach
eastward.

Monday, Memorial Day, appears to carry the highest heat threat.
Model guidance is peaking out the ridge at 595 to 596 dam, and is
painting triple digit readings for all interior areas with heat
index values in the 115 to 120 degree range. This would support an
excessive heat warning for the day. Record high temperatures may
be tied or broken, especially on Memorial Day. Monday night
temperatures will remain warm with lows in the upper 70s across
the Northern Ranchlands to the lower 80s across the Lower Rio
Grande Valley. The record high in the Brownsville area for May 27
was 99 degrees in 1973; in Harlingen 90 degrees in 2011; and in
the McAllen area 107 degrees in 1973. Heat index values after
Monday will tend to be slightly lower, but will still support
heat advisories.

The 500 mb ridge may flatten slightly as short waves traverse
west to east over Central and South Texas through the week. There
is a slight chance of showers and a few thunderstorms rolling east
off the Sierra Madre Oriental chain in Mexico and into the Upper
Valley Monday and Tuesday evenings. We`ve seen this phenomenon
before, and it shows up mostly Monday and to some extent Tuesday
evening. In general, however, the mid-level ridge itself will
shift slightly to the west through the week so that it is no
longer directly over or on top of the region. There will be plenty
of sun and readings in the century mark the remainder of the
week, with moderate to breezy southeast winds, but Monday looks
like the hottest of the bunch.

&&

.AVIATION...
-- Changed Discussion --
(06Z TAFS)
Issued at 1237 AM CDT Sun May 26 2024

A mix of VFR/MVFR ceilings and moderate southeast winds prevail
across Deep South Texas early this morning. Widespread MVFR
ceilings are expected to develop overnight. Low cloud decks then
should decrease after sunrise, with VFR conditions returning to
all RGV aerodromes by mid-morning. Some intermittent visibility
reductions are possible through the period, as haze/mist could
briefly drop visibility to 5-6 miles, though confidence is too low
to include in the TAF. Light to moderate winds overnight will
increase and become gusty later this morning into the afternoon.
-- End Changed Discussion --

&&

.MARINE...
Issued at 105 PM CDT Sat May 25 2024

Tonight through Sunday night....Moderate winds via a relatively
tight pressure gradient will result in potential SCEC conditions
during the day on Sunday, particularly over the Laguna Madre.

Monday through Thursday night...Moderate to occasionally fresh
southeast breezes and moderate to slightly elevated wave heights
will prevail. High pressure will remain steady over the Gulf, with
the gradient slightly tighter at times due to lowered pressure
inland. Small craft should exercise caution conditions will
develop on occasion.

&&

.CLIMATE...

Record High Minimums for tonight

Brownsville 81F in 2000
Harlingen 80F in 2000
McAllen 81F in 2017

Record Daytime Highs for Sunday May 26, 2024

Brownsville 97F in 2018
Harlingen 99F in 2018
McAllen 102F in 2017

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
BROWNSVILLE             82  97  81  95 /   0   0  10   0
HARLINGEN               80 100  78  98 /  10  10  10   0
MCALLEN                 83 104  81 100 /  10  10  10   0
RIO GRANDE CITY         81 106  80 101 /  10  20  20  10
SOUTH PADRE ISLAND      83  88  83  87 /   0   0  10   0
BAYVIEW/PORT ISABEL     82  95  80  93 /   0   0  10   0
-- End Changed Discussion --

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
TX...Heat Advisory until 11 AM CDT this morning for TXZ248>255-351-
     353>355.

     Excessive Heat Warning from 11 AM this morning to 9 PM CDT this
     evening for TXZ248>255-351-353>355.

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

GM...None.
-- End Changed Discussion --
&&

$$

SHORT TERM...23-Evbuoma
LONG TERM....54-BHM
AVIATION...63-KC