Heat Advisory 21, NWS Brownsville, TX

096 
WWUS74 KBRO 222349
NPWBRO

URGENT - WEATHER MESSAGE
National Weather Service Brownsville TX
649 PM CDT Thu Aug 22 2024

TXZ249>255-351-353>355-230100-
/O.EXP.KBRO.HT.Y.0021.000000T0000Z-240823T0000Z/
Jim Hogg-Brooks-Inland Kenedy-Starr-Southern Hidalgo-Inland
Willacy-Inland Cameron-Coastal Kenedy-Northern Hidalgo-Coastal
Willacy-Coastal Cameron-
Including the cities of McAllen, Rio Grande City, Hebbronville,
Mission, Harlingen, Port Isabel, Raymondville, Roma, Port
Mansfield, San Manuel, Edinburg, Weslaco, Sarita, Brownsville,
Falfurrias, Pharr, and Laguna Vista
649 PM CDT Thu Aug 22 2024

...HEAT ADVISORY WILL EXPIRE AT 7 PM CDT THIS EVENING...

Heat indices have fallen below 111 degrees and will continue to 
decrease this evening.

$$

60-BE

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1203 AM CDT Thu Aug 22 2024

...New AVIATION...

.SHORT TERM...
(Tonight through Thursday night)
Issued at 247 PM CDT Wed Aug 21 2024

Deep South Texas will remain under the influence of mid/upper level
ridging, resulting in rain-free conditions and above normal
temperatures for mid to late August. After one of the hottest days
of the year, low temperatures tonight will fall into the 70s and low
80s region wide. Some patchy fog cannot be ruled out, but should
quickly dissipate early tomorrow morning. Another hot day is
expected on Thursday as the center of the mid level ridge remains
over Texas, with high temperatures ranging from around 90 degrees
along the Lower Texas beaches to around 103 degrees across the
Mid/Upper RGV and Rio Grande Plains. In combination with the
humidity, heat indices will range from 105-114 degrees during the
afternoon hours. A Heat Advisory will likely be needed for portions
of the region Thursday afternoon, particularly areas along and east
of US-281 where higher dew points will reside. Otherwise, another
mild and humid night with lows in the 70s and low 80s is expected
once again Thursday night.

&&

.LONG TERM...
(Friday through next Wednesday)
Issued at 247 PM CDT Wed Aug 21 2024

The big picture has changed little over the past couple of days:
500 mb ridge ("heat dome" remains anchored across Texas Friday
into early Saturday, with the core nudging into the lower
Mississippi Valley later Saturday while tipping over to an axis
from Missouri/Arkansas southwest into the Permian Basin. As this
happens, the previously mentioned 500 mb upper level low/trough
slides westward underneath the 500 mb ridge as it spreads eastward
toward the lower Ohio Valley. The west side of the low reaches the
Texas coast Sunday evening and eases across south/central Texas
later Monday through Tuesday before weakening somewhere in west or
central Texas by Wednesday.

Continued typical late August heat and plenty of sunshine with
nothing more than an isolated sea breeze shower along/near
IH-69E/US 77 Saturday afternoon will be the story, before somewhat
deeper moisture begins to arrive Sunday mainly across the Gulf
Sunday and eases inland Sunday night through Tuesday before
potentially nudging farther west on Wednesday.

In terms of sensible weather...another triple digit day Friday
west of IH-69E/US 77 afternoon but with a pocket of drier low/mid
level air expect daytime humidity to lower and heat index values
be just a few degrees above actual temperatures (i.e. 105-109).
Saturday should be similar, with slightly higher atmospheric
moisture in the column, apparent temperatures may slide to
advisory levels (111) but only briefly...so not expecting advisory
conditions either afternoon.

As the front (subsident) side of the upper level trough arrives
late Sunday, atmospheric cooling begins which should help with
late morning/early afternoon cumulus buildups and nudge
temperatures down a degree or two, with most areas peaking in the
mid to upper 90s. With area being on the subsident side of the
approaching trough, rain chances/coverage will remain low...though
higher than Saturday and focusing in the lower/mid Valley though
cannot rule out some coverage across the Brooks/Kenedy ranches.

The more difficult part of the forecast arrives Monday and
continues through Wednesday. Region moves to the more favorable
back (convergent) side of the 500 mb trough for rainfall and lower
temperatures due to cooling atmospheric temperatures and more
cloud cover (rapid buildups) Monday...so heat will reduce to or
just below late month averages through the period.

The idea of mainly late morning through afternoon scattered
showers/storms, jumping quickly inland along the sea breeze, is on
target. However, with the trough remaining/becoming disorganized
while moving west, picking out locations for potentially locally
heavy rains on Days 5-7 is virtually impossible...especially given
model differences that cannot yet be resolved. Model blends smooth
out these differences which is a reasonable compromise, with
30-50 percent rain chances beginning just inland from the beaches
and increasing through the afternoon/sunset before quickly ending
or dissipating soon after. Unknown, however, is exactly where and
how much rain might fall in more potent cells. So...while area-
wide QPF is rather paltry for this period (less than 0.5 inch),
expect some locations to see 2-3 inches in such cells each
afternoon, especially Tuesday and Wednesday.

Details will be ironed out over the weekend.

&&

.AVIATION...
(06Z TAFS)
Issued at 1200 AM CDT Thu Aug 22 2024

High pressure in the middle layers of the atmosphere will produce
VFR at the aerodromes through the next 24 hours.

&&

.MARINE...
Issued at 247 PM CDT Wed Aug 21 2024

Tonight through Thursday night...Light to moderate winds and low
seas will prevail over the Gulf Waters and Laguna Madre as surface
high pressure persists over the western Gulf of Mexico.

Friday through Monday Night...More copacetic weather for boaters
and fishers through Saturday evening before isolated to scattered
showers/thunderstorms arrive toward the shelf waters early Sunday,
and more coverage and perhaps likely early Monday through
Wednesday, with diurnal trends favoring initial onset after
midnight each morning, continuing through mid to late morning
before nearshore and Laguna activity "jumps" inland along the sea
breeze by afternoon with continued activity beyond 20nm out.

Outside of any organized convection, slight seas and light
generally east to southeast winds will be the rule, with the usual
10-15 knot afternoon sea breeze or enhancement along the coast
through Laguna Madre each day.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             79  96  79  95 /   0  10   0  20
HARLINGEN               75  97  75  96 /   0  10   0  20
MCALLEN                 79 102  78 101 /   0   0   0  10
RIO GRANDE CITY         77 101  76  99 /   0   0   0   0
SOUTH PADRE ISLAND      83  90  82  89 /   0   0   0  10
BAYVIEW/PORT ISABEL     78  94  77  92 /   0   0   0  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...None.

&&