338
FXUS64 KBRO 221118 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
618 AM CDT Wed May 22 2024

...New AVIATION...

.SHORT TERM...
(Today through Thursday)
Issued at 310 AM CDT Wed May 22 2024

500 mb high pressure centered along the upper east coast of
Mexico, and extended over the BRO CWFA, will remain the dominant
weather feature in play through the period. This will continue to
have the effect of not only producing dry weather, but also well
above normal daytime high temperatures. Compared to recent
observations, NBM guidance appeared slightly too cool for high
temperatures today, so increased these a couple of degrees. This
yielded heat index vales at, or slightly above, HEAT ADVISORY
criteria for all of Deep South Texas and the Rio Grande Valley
except the island portions of Cameron, Willacy, and Kenedy
counties today, and as a result, a HEAT ADVISORY is in effect for
this specific area for half a dozen hours. An additional HEAT
ADVISORY is likely to be needed on Thursday for the same, if not
slightly smaller, area.

&&

.LONG TERM...
(Thursday night through Tuesday)
Issued at 310 AM CDT Wed May 22 2024

Key Messages:

- Extreme and Dangerous Heat through the weekend.
- Record daily highs and overnight Max Minimums in jeopardy.

No let up in the heat with all models trending hotter Friday-
Monday. The weekend looks likely the hottest overall with
potentially deadly excessive heat as mean heat index values of
115- 118 degrees and peak values potentially exceeding 120 degrees
are indicated by the latest consensus model output. Record heat
is also expected with this latest heat wave with daily maximums as
well as nightly overnight (highest Minimum Temperatures)being
threatened.

The northern side of a 500mb subtropical ridge remains anchored
through early next week with a building heat dome over North Mexico
and South Texas. 850mb temperatures continue to climb with the
latest model suite indicating  Friday at 23-27C, Sat-Mon 26-31C
which exceeds the 95 percentile and on some days all time daily
Maxes could be exceed. The anomalous subtropical ridge and the high
850mb temps will allow ambient temperatures to soar well over 100
degrees for much of the CWA with exception of the immediate coastal
sections. Along and west of I-69 highs range from 103 to 111F Sat-
Monday with 88-102 from the beaches to I-69E/C. The modest and
breezy southerly flow and warm Gulf of Mexico sea surface
temperatures continue pumping in elevated dew points. As we know,
the extreme heat combined with the elevated dewpoints   will be a
mix for dangerous and potentially deadly heat indices which will
reach and in some locations possibly exceed 120F degrees. Expect
daily heat advisories Friday-Monday with a medium to high (50-70%)
probability of excessive heat warnings Saturday-Monday.  No relief
overnight with latest temperature guidance indicating lows only
reaching 77-82 degrees and this may be conservative especially in
the urban heat island locations of McAllen, Harlingen, and
Brownsville.

To say the least, no rain is in the forecast with subsidence
provided by the high pressure ridge keeps the mid-layers very dry
(below 30% RH) and maintains a strong warm cap in place. Any
thunderstorms that form over and move east off the Sierra Madre of
NE Mexico will have a very difficult time maintaining integrity
as they run into the stable conditions east of the Rio Grande.

&&

.AVIATION...
(12Z TAFS)
Issued at 611 AM CDT Wed May 22 2024

MVFR to VFR will continue to be the rule at the aerodromes through
the next 24 hours.

&&

.MARINE...
Issued at 310 AM CDT Wed May 22 2024

(Today through Thursday): Buoy 42020 reported southeast winds
around 16 knots gusting to around 19 knots with seas slightly
under 4.5 feet with a period of 6 seconds at 150 CDT/650 UTC. An
enhanced pressure gradient will exist along the Lower Texas Coast
during the period courtesy of high pressure over the western Gulf
of Mexico interacting with thermal low pressure over inland
Mexico. Moderate to breezy winds and generally moderate sea are
likely, as is Small Craft Should Exercise Caution for portions to
all of the lower Texas coastal waters.

(Thursday night through Tuesday): A moderate pressure gradient is
forecast to persist over the Western Gulf of Mexico through the
week and next weekend. Broad surface ridge centered over the
Southwest Atlantic and extending over the Gulf will combine with a
thermal low pressure area over NE Mexico maintaining a daily
moderate to occasionally gusty southeast wind and a moderate sea.
No rain is expected as an upper level ridge suppresses the chance
of thunderstorms the next several days.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             96  81  95  81 /  10   0   0   0
HARLINGEN               99  78  97  78 /   0   0   0   0
MCALLEN                101  80 100  81 /   0   0   0   0
RIO GRANDE CITY        104  79 103  79 /  10   0   0   0
SOUTH PADRE ISLAND      89  82  87  82 /   0   0   0   0
BAYVIEW/PORT ISABEL     94  79  93  80 /   0   0   0   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory from 1 PM this afternoon to 7 PM CDT this evening
     for TXZ248>255-351-353>355.

GM...None.
&&

$$