838
FXUS64 KBRO 091740 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1240 PM CDT Sun Jun 9 2024

...New AVIATION...

.SHORT TERM...
(Today through Monday)
Issued at 249 AM CDT Sun Jun 9 2024

Key Messages:

* Continued hot and humid today...slightly less hot Monday amid
  slight pattern breakdown and potential sea breeze developing

* Widespread major HeatRisk today; Moderate to major HeatRisk on
  Monday

* Low, yet non-zero probability of a rogue shower or thunderstorm
  Monday afternoon amid a sea breeze developing (15-30% chance PoPs
  across the area)

* Outside of convective chances on Monday, favorable marine
  conditions look to persist with light winds and seas

The short term forecast period will feature the weakening or
relaxing of what has been an anomalously strong and persistent early
season heat ridge, which has plagued South Texas (since late May)
and most recently the western U.S. with relentless heat that
includes heat episodes, heat waves, and record-shattering
temperatures. Global forecast models and full suite of ensembles
continue to advertise the weakening, albeit for a brief period, of
the 500 mb ridge today into Monday. Associated with this will be a
cold front that will continue to translate southward from the
central Plains into the southern Plains. The frontal boundary is
expected to slow/stall over central or north-central Texas during
the day on Monday. Given this overview/situation, a notable airmass
change is not expected to take place over Deep South Texas and the
Rio Grande Valley despite changes especially noted in the mid to
upper levels of the atmosphere. That said, a very warm to hot and
humid airmass will remain intact over the region through Monday.

Forecast highs today are expected to range from the upper 90s to
lower 100s under mostly sunny to  partly cloudy skies. With dewpoint
(Td) temperatures holding in the 70s, heat indices (apparent "Feel
Like" temperatures) will be very borderline between a Special
Weather Statement (SPS) and a Heat Advisory with values expected to
range between 105-110F degrees. Hottest locations could see heat
indices up to 114F degrees, however, coverage will be very local.
Given that these temperatures, if realized, will only occur for an
hour or two and after collaboration with CRP (Corpus Christi`s
Weather Forecast Office), have opted to hold off issuing a Heat
Advisory and will let the day shift further evaluate the situation.
That said, will issue a Special Weather Statement (SPS) for Inland
Cameron, Hidalgo, and Starr Counties. That`s where confidence is
greatest that we`ll see heat indices range between 108-115F degrees.

Tonight will feature another warm and muggy night with overnight
lows expected to hold between the mid 70s to lower 80s under
increased cloud coverage or partly to mostly cloudy skies.

Monday, high temperatures will be a few degrees cooler (subtle
change to the pattern described above). Have nudged high
temperatures down a couple degrees from the NBM. That said, it will
still be very warm and humid with highs mainly in the mid to upper
90s with maybe a few 100s. Heat indices will be a similar situation
to today (borderline SPS to Heat Advisory for parts of the area).
The other weather concern for Monday will be with regards to
convection chances. Forecast models and ensembles continue to
suggest the low chance/potential of an isolated shower or
thunderstorm developing somewhere over the region during the day on
Monday as the aforementioned cold front reaches central Texas and
precipitable water (PWAT) values approach 2 inches, despite having a
weak to non-existent shortwave overhead. Forcing will be limited,
but if we could get enough surface convergence Monday afternoon as
winds are expected to become more easterly (sea breeze), that could
help to weaken the cap and trigger a rogue sea breeze shower or
thunderstorm somewhere over our CWFA. Have decided to go with a
blended approach amongst guidance and have 15-30% chance PoPs over
the local forecast area for Monday. Otherwise, expect for rain-
free conditions to continue with ideal weather, especially for the
beachgoers.

&&

.LONG TERM...
(Monday night through Saturday)
Issued at 249 AM CDT Sun Jun 9 2024

A weak shortwave may help kick up convection across the brush
country and upper RGV Monday night before the persistent mid-
level ridge returns Tuesday through the remainder of the long term
period. A 500mb low rounds the northern edge of the ridge from
the panhandle into the Gulf. The GFS has this low getting into the
Gulf by Wednesday night, while the Euro slows it until Friday.
Either way, most model guidance has broad low pressure across the
Central Gulf and keeps us to the west of the 500mb low through the
week, but do increase moisture across the Gulf through the long
term with a weak pressure gradient. In a light wind regime, expect
the sea breeze to develop every day, potentially clipping highs
across coastal counties compared to the past couple of weeks and
limiting peak Heat Indices. Highs still reach 97-102 east to west,
with lows 75-79.

As of right now, the best chance of rain in the long term remains
with any Sierra Madre convection Monday night. Beyond that, it
will look very summer-like, with the chance of streamer showers
along the coast each morning and isolated convection along the sea
breeze each afternoon. Current POPs are low, generally at or below
15 percent, but wouldnt be surprised to see at least one or two
cells each day roaming along with the sea breeze into the
afternoon.

&&

.AVIATION...
(18Z TAFS)
Issued at 1240 PM CDT Sun Jun 9 2024

Overall...same forecast (from Saturday) but different day. Few to
scattered VFR cumulus this afternoon at the lower Valley terminals
with any low clouds clearing out at McAllen by mid afternoon.
We`ll also see the usual east to west movement of the enhanced
southeast flow with gusts around 20-22 knots at Brownsville and
Harlingen through sunset...and 24 knots at McAllen just before
sunset for a couple hours after.

For the overnight...other than scattered MVFR fractus
clouds...we`ll need to keep an eye on any residual mid/high
clouds from any convection that develops in central/south central
Texas as weak short wave energy rotates through the general upper
level ridging overnight. Not expecting any of this convection or
residual rain and lower clouds to reach the Valley terminals at
this point. Quick develop scattered-broken low VFR cumulus again
Monday morning with slightly lower southeast wind speeds.

&&

.MARINE...
Issued at 249 AM CDT Sun Jun 9 2024

Now through Monday...High pressure and a weak pressure gradient will
result in favorable marine conditions today through Monday. Light to
moderate east-southeasterly winds will result in light seas. There
is a chance, albeit low, of an isolated shower or thunderstorm
developing on Monday.

Monday Night through Saturday...A weak pressure gradient maintains
generally light southeasterly to easterly flow through the long
term period resulting in seas of 2 to 3 feet. Broad low pressure
gradually builds across the Central Gulf, likely increasing the
chance of streamer showers or convection each night and morning
into next weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             96  82  95  79 /  10   0  20  10
HARLINGEN               99  78  96  75 /  10   0  20  10
MCALLEN                100  81  97  79 /  10   0  20  20
RIO GRANDE CITY        101  79  97  77 /   0  10  20  20
SOUTH PADRE ISLAND      89  83  86  82 /  10  10  20  10
BAYVIEW/PORT ISABEL     94  81  92  78 /  10   0  20  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$


AVIATION Update...52-Goldsmith