-- Discussion containing changed information from previous version are highlighted. --
876
FXUS64 KBRO 091719 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1219 PM CDT Thu May 9 2024

...New AVIATION...

.SHORT TERM...
(Today through Friday)
Issued at 321 AM CDT Thu May 9 2024

Key Messages:

- Triple-digit temperatures and heat index values are expected
across Deep South Texas this afternoon.

- A Heat Advisory is in effect for portions of the region this
afternoon.

- Remember to take the necessary precautions against the heat to
limit the risk of heat-related impacts and illnesses. Never leave
children or pets in vehicles, drink plenty of fluids to stay
hydrated, and take frequent breaks if spending a prolonged period
outside.

Today will be the hottest day of the week across Deep South Texas,
with daily record high temperatures likely to be tied or broken at
Brownsville (97 in 1998), Harlingen (100 in 1998), and McAllen (103
in 1998). Guidance continues to indicate 850 mb temperatures will
approach the warmest values of the week, ranging from 27-29C this
afternoon. Additionally, probabilistic guidance maintains a high
chance (70% or greater) for most of the region to reach at least 100
degrees this afternoon, with the exception being along the immediate
coast and Lower Texas beaches.

The latest satellite and surface observations reveal the return of
widespread stratus clouds and dew points in the mid to upper 70s.
This is due to the west/northwest retreat of the dryline late
Wednesday evening. Despite the mild and humid start to the day, this
morning`s low clouds are expected to clear from west to east by mid
to late morning as low level winds (around 925-850 mb layer) begin
to shift to the west and transport warmer, drier air. Downward
momentum will allow for the warmer, drier air to reach the surface,
and the aforementioned dryline will begin to push east across Deep
South Texas through early this afternoon. High res guidance
continues to suggest the dryline will extend as far east as the I-69
corridor, which would temper the heat index as dew points fall into
the 50s and 60s. Despite lower dew points, it will still be very hot
this afternoon with high temperatures ranging from 103 to 109
degrees along/west of I-69. For areas east of the dryline, dew
points will remain in the 70s and high temperatures will range from
the mid 80s along the lower Texas beaches to around 103 degrees
along I-69. In combination with the higher humidity, heat index
values will once again approach 111-114 degrees for portions of
Kenedy, Willacy, and Cameron counties. Some guidance does suggest
heat index heat index values may approach 115-116 degrees this
afternoon along the I-69 corridor, but should only occur for one
hour, which is just shy of the 2 hour criteria for an Excessive Heat
Warning. However, this will be highly dependent on the eastward
extent of the dryline this afternoon and will need to be closely
monitored.

Fortunately, the arrival of a weak cold front on Friday will provide
some relief from the oppressive midweek heat. The latest guidance
suggest the frontal boundary will be slow to arrive on Friday,
likely during the afternoon and evening hours, but will at least
bring an end to the triple-digit heat. Temperatures on Friday should
be closer to normal for early May, ranging from the upper 80s along
the immediate coast to mid 90s across the Rio Grande Plains. Outside
of limited rain chances (20% or less) across the Rio Grande Plains,
most of the region will remain rain-free on Friday.

&&

.LONG TERM...
(Friday night through Wednesday)
Issued at 321 AM CDT Thu May 9 2024

The weak cold front is expected to stall and linger along the Rio
Grande River area Friday evening into the first half of the
weekend. While the surface winds will shift to the northeast
behind the front Friday night, it will be short lived. The winds
are expected to quickly shift back towards the east on Saturday as
surface high pressure slides eastwards. Temperatures are expected
to be more seasonable on Saturday with highs in the mid to upper
80s to around 90. Lows Friday night and Saturday night will be in
the 70s. Temperatures start to heat up again on Sunday as the
stalled frontal boundary pushes northward as a warm front and
steady southeast flow returns. As such, temperatures will be back
to being above normal with highs mostly in the mid to upper 90s
and some places in the triple digits by Monday and lasting through
the rest of the period. Meanwhile, the overnight low temperatures
are expected to be in the 70s.

Weak overrunning will support isolated to scattered showers and
thunderstorms over the weekend. The return of the onshore flow on
Sunday could also aid in the development of showers and
thunderstorms on Sunday and Monday. SPC has the entire CWA in a
general thunderstorm outlook for days 2 and 3 (Friday night through
Saturday night).

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 1214 PM CDT Thu May 9 2024

While VFR conditions are expected to continue for most of the
afternoon and into the evening at the TAF sites. A return of MVFR
ceilings is expected for HRL and BRO during the overnight hours as
low-level clouds move in. While southeasterly winds are also
expected to continue a BRO, a dryline is expected to create a
shift in the wind direction towards the west northwest around 16Z
for MFE and 18Z for HRL. However despite the change in wind
direction, winds are expected to be light. Persistent haze is
likely to keep the visibilities down through the TAF period to
about 5 or 6 miles.
-- End Changed Discussion --

&&

.MARINE...
Issued at 321 AM CDT Thu May 9 2024

Today through Friday...Light to moderate southeast winds and
moderate seas will prevail through tonight. Patchy fog over the Gulf
waters and Laguna Madre will be possible each morning, and haze may
also be observed through Friday. Brief periods of Small Craft
Exercise Caution conditions will be possible this afternoon over the
Laguna Madre. A weak cold front will arrive on Friday and result in
winds shifting to the east.

Friday night through Wednesday...Moderate northeasterly to easterly
winds and moderate seas are expected Friday night into Saturday with
the passage of a weak cold front. Southeast winds are then expected
to develop on Sunday with moderate winds and seas prevailing along
the Lower Texas Coast through the rest of the period. Small Craft
Exercise Caution conditions may be needed at times.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE            103  78  92  77 /   0   0   0  10
HARLINGEN              104  77  92  74 /   0   0   0  10
MCALLEN                107  79  96  77 /   0   0  10  10
RIO GRANDE CITY        107  78  95  75 /   0   0  10  20
SOUTH PADRE ISLAND      86  77  83  77 /   0   0   0  10
BAYVIEW/PORT ISABEL     98  77  87  75 /   0   0   0  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
TX...Heat Advisory until 7 PM CDT this evening for TXZ251-254-255.

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

$$

SHORT TERM...22-Garcia
LONG TERM....63-KC
AVIATION...64-Katz