-- Discussion containing changed information from previous version are highlighted. --
637
FXUS64 KBRO 271147 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
647 AM CDT Mon May 27 2024

...New AVIATION...

.SHORT TERM...
(Today through Tuesday)
Issued at 217 AM CDT Mon May 27 2024

Key Messages:

* Excessive, Dangerous, Record-Breaking Heat today
* High Rip Risk through late this evening
* Marginal Severe Weather Risk Northwest portions this
  afternoon/evening

Mid-level ridging (595 dam) anchored over Mexico will provide strong
subsidence across Deep South Texas and the Rio Grande Valley.
Dangerous heat will continue today with triple-digit temperatures
ranging from around 100 degrees along the I-69E corridor to near 108
degrees across the Rio Grande Plains. High temperatures will range
from the mid to upper 80s at the beaches to the 90s near the coast.
Record high temperatures may be tied or broken (see climate section
below). Due to steady southeast surface flow, dew points climbing
well into the 70s will support elevated heat index values ranging
from 115 to 122 degrees for a few hours this afternoon. Therefore,
an Excessive Heat Warning in effect for today.

Some convection may develop over the Sierra Madre Oriental Range and
drift towards the Rio Grande Plains this afternoon as a weak
shortwave traverses around the periphery of the 500 mb ridge. The
latest GFS is more robust with convection developing and then moving
into the Rio Grande Plains around sunset. However, confidence
remains low on convection coverage this afternoon and evening due to
the spread in the current CAM models. Lean towards a mix of the NBM
and ConsShort for pops for today into tonight. In any case, isolated
stronger storms could deliver large hail and strong, damaging winds
this afternoon into the late evening. Any of the heavier storms may
produce brief downpours and could result in a quick inch of rain.
SPC has portions of the Rio Grande Plains, Brush Country, and Upper
Valley in a marginal severe risk for late this afternoon into the
evening. While, the Mid to Lower Valley and the coast remain in a
general thunderstorm outlook.

Low temperatures tonight will remain warm with lows in the upper 70s
across the Northern Ranchlands to the lower 80s across the Lower Rio
Grande Valley.

Models continue to indicate the center of the 500 mb subtropical
ridge shifting slightly to the south-southwest and should allow for
a minor lowering of high temperatures on Tuesday. However, daytime
high temperatures and heat indices will remain well above normal on
Tuesday. Highs on Tuesday are expected to range from the mid to
upper 90s across the coastal counties to the triple digits (100 to
104 degrees) across the Mid to Upper Valley and the Rio Grande
Plains. There is a medium (40-60 percent) probability of Heat
advisories occurring Tuesday afternoon. Also, the Experimental NWS
Heat Risk Index continues to show Major to Extreme (4-5 out of 5) on
Tuesday for the risk of heat-related impacts.

Another opportunity of rain (low chance) is on Tuesday afternoon as
convection from the higher terrain of Mexico drifts towards the Rio
Grande Plains. SPC has most of Deep South Texas in a general
thunderstorm outlook for Tuesday.

The persistence moderate southeast winds over the Gulf of Mexico
will continue to drive a moderate swells towards the Lower Texas
Coast through the period. Therefore, a continuation of a High Rip
Current Risk is expected through this evening.

&&

.LONG TERM...
-- Changed Discussion --
(Tuesday Night through Sunday)
Issued at 217 AM CDT Mon May 27 2024

The aforementioned 500 mb subtropical ridge will remain the
dominant feature over the BRO CWFA through the period, with the
center of this feature varying from the upper east coast of Mexico
to just south of the Baja Peninsula. Although dry weather will
prevail through a majority of the time for Deep South Texas and
the Rio Grande Valley, isolated showers and thunderstorms are
occasionally possible, and primarily over the northern ranchlands
(Zapata, Jim Hogg, Brooks, and Kenedy counties). This will be due
to convection initiating over neighboring Mexico courtesy of mid-
level shortwaves and then migrating into ranchland area.

Additionally, well above normal daytime high and overnight low
temperatures will also occur. Forecast heat indices for the long
term forecast period suggest that a HEAT ADVISORY is most likely
for inland portions of the BRO CWFA Friday and Saturday, with a
SPECIAL WEATHER STATEMENT Wednesday, Thursday, and Sunday in lieu
of the HEAT ADVISORY. Ultimately, will see if this regime holds as
the new work week progresses.

Finally, the intensity of the pressure gradient, with thermal low
pressure over Mexico interacting with building high pressure over
northeast Mexico, may result in a WIND ADVISORY for the three
immediate coastal counties (Cameron, Willacy, and Kenedy) on
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
(12Z TAFS)
Issued at 636 AM CDT Mon May 27 2024

MVFR conditions and light southeast winds prevail across Deep
South Texas early this morning. Widespread HZ/BR have developed
overnight and may linger across the area through at least mid to
late morning. VFR conditions should return to all RGV aerodromes
by late morning. Some intermittent visibility reductions are
possible through the period, as haze/mist could briefly drop
visibility to 4 to 6 miles. Light winds this morning will
increase and become gusty later this morning into the afternoon.
Some convection may develop late this afternoon into this evening
over the higher terrain of Mexico and may drift towards the
region. Some convection could reach MFE late in the period but
will not mention at this time due to low confidence.
-- End Changed Discussion --

&&

.MARINE...
(Today through Tuesday)
Issued at 217 AM CDT Mon May 27 2024

Low to moderate southeast winds and moderate to slightly enhanced
wave heights will prevail through the period. High pressure
across the Gulf will provide the driving force for the seasonal
winds. Small craft may at times need to exercise caution.

(Tuesday Night through Sunday)
Steadily increasing winds and building seas will occur along the
Lower Texas Coast through the period. This will be due to thermal
low pressure over inland Mexico gradually interacting more
intensely with high pressure building over the northeast Gulf of
Mexico. Small Craft Should Exercise Caution be will a certainty,
with Small Craft Advisory becoming more likely beginning Friday
and continuing through the end of the period.

&&

.CLIMATE...
Issued at 217 AM CDT Mon May 27 2024

Record Highs for today May 27, 2024

Brownsville 99 in 1973 (Forecast high 99)
Harlingen 100 in 2018 (Forecast high 101)- break in the climate record
McAllen 107 in 1973 (Forecast high 104)

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             97  82  96  81 /  10  10  10   0
HARLINGEN              100  79  98  78 /  10  10  10  10
MCALLEN                104  82 101  80 /  20  10  10  10
RIO GRANDE CITY        104  80 102  78 /  20  20  10  20
SOUTH PADRE ISLAND      87  82  87  82 /  10  10  10  10
BAYVIEW/PORT ISABEL     94  80  93  80 /  10  10  10  10

&&

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

     Excessive Heat Warning from 11 AM this morning to 8 PM CDT this
     evening for TXZ248>255-353.

     Heat Advisory until 8 PM CDT this evening for TXZ351-354-355.

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

GM...None.
&&

$$

SHORT TERM...63-KC
LONG TERM....66-Tomaselli
AVIATION...63-KC