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Area Forecast Discussion (AFD)

Issued by Brownsville/Rio Grande Valley, TX (BRO)

FXUS64 KBRO 231738 AAC

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1238 PM CDT Mon Sep 23 2019

.DISCUSSION...Updated for latest aviation discussion below.


.AVIATION...VFR conditions prevail this afternoon and into the
overnight hours. Isolated showers and a possible thunderstorm
along a weak sea breeze are possible but with probabilities rather
low will leave out for the afternoon hours. For the overnight
period , a surge in moisture with the approach of mid-level 
disturbance could lead to isolated to scattered showers or a
possible thunderstorm which might move into the vicinity of KHRL 
a KBRO after midnight through sunrise Tuesday. Light southeast 
winds expected today and tonight. 


.PREV DISCUSSION... /issued 906 AM CDT Mon Sep 23 2019/ 

A few cosmetic changes made to the forecast for today and tonight.
Rain chances look minimal so will indicate isolated convection
along the sea breeze for the afternoon, possible not working its
way through the western third of the CWA with limited moisture
depth the weak state of the sea breeze indicated by the CAMs. Much
of the convection should wane by the evening with just a few
lingering or on-going activity offshore overnight. High and low 
temperatures were adjusted slightly following persistence from 
readings over the last several days. Forecast will be out soon. 

PREV DISCUSSION... /issued 623 AM CDT Mon Sep 23 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...No changes needed to the previous set of TAFs. VFR 
will continue today as winds become moderate with breezy gusts. 
Isolated convection is forecast, but continues to be excluded from
the latest iteration of TAFs. Cloud cover may be more widespread 
tonight such that MVFR may occur with light winds at the surface.

PREV DISCUSSION... /issued 417 AM CDT Mon Sep 23 2019/ 

SHORT TERM (Today through Tuesday): Autumn began at 250 AM CDT this 
morning, and once again, Deep South Texas and the Rio Grande Valley 
survived a sweltering summer that was punctuated by a few heavy rain 
events, the most significant of which occurred on June 24th into 
June 25th. Although the magnitude of that event will not be repeated 
during the short term portion of this forecast, deep tropical 
moisture will interact with the approach of an inverted 500 mb 
trough from the east to produce isolated to scattered showers for 
the entire BRO CWFA. The recent trend of above normal daytime high 
and overnight low temperatures will continue given the expected 
relatively low rain chances and limited cloud cover. 

LONG TERM (Tuesday Night through Sunday): The mid-level pattern 
to begin the long term period will showcase a large cutoff low 
over the northern Baja California peninsula and a 590 dam ridge 
centered across the eastern Gulf of Mexico. In-between these 
synoptic features, a general mid-level weakness, with a possible 
weak embedded easterly wave, will sit atop South Texas and the 
western Gulf of Mexico. This weakness will get sheared out late 
in the week as the cutoff low becomes more progressive with a
movement towards the west-northwestward and starts to open back
up into a trough. At the same time, an another upper level low 
centered over the Bahamas should help to allow for the 500 mb 
ridging to build westward for the upcoming weekend. However,
the latest model solutions do diverge slightly on the strength
of the increasing 500 mb heights over the area. In fact, the
latest GFS has an another weak impulse move over the region on 

Local precipitation chances will be quite limited despite the 
general mid-level weakness aloft during midweek. The latest 
modeled time heights show dry air aloft holding on across the 
area. Models do show pockets of high clouds but not too much 
additional forcing besides the typical seabreeze pushing from off 
the coast. In fact, Wednesday looks to trend drier with pops 
around 10% across the eastern half of the region as the low-level 
moisture is less impressive. The rest of the week includes slight 
chance to chance pops along the seabreeze as the low-level 
moisture increases.

Expect for above average temperatures to continue through the
long term period. The ECMWF MOS output continues to run higher 
regarding the temps with slightly stronger ridging, especially 
late in the period. I will continue to trend the temperatures with
a blend that leans closer to the ECMWF guidance. Expect for an 
increase in the low-level moisture advection late this week and 
into the upcoming weekend. This shall help to raise overnight lows
to even muggier levels and peak afternoon heat index values into 
the 105 to 110 degree range.

The tropical Atlantic Basin remains active with the National
Hurricane Center monitoring TS Jerry, TS Karen and TD 13. TS Jerry
is expected to recurve to the N and NE moving into the northern 
Atlantic Thur and Fri. Meanwhile, TS Karen is expected to continue
moving in a general northerly direction moving north of Puerto 
Rico on Thurs and Fri. Please refer to the latest outlooks and 
statements from the National Hurricane Center concerning the 
future progress of these tropical cyclones.

MARINE (Now through Tuesday): Buoy 42020 reported southeast 
winds around 12 knots gusting to around 14 knots with seas 
slightly under 5 feet with a period of 9 seconds at 150 CDT/650 
UTC. Rough swells from the east will continue to produce Small 
Craft Exercise Caution for the Gulf of Mexico waters from 20 to 60
nautical miles offshore today and tonight. The swell will subside
slightly on Tuesday, allowing moderate seas for all of the lower 
Texas coastal waters at that time. Wind-wise, light to moderate 
winds are anticipated for the entire period.

Tuesday night through Friday: Broad surface ridging concentrated
across the Gulf of Mexico will maintain a modest to moderate 
surface pressure gradient and steady southeasterly winds across 
the Lower Texas coastal waters through the period. An easterly 
fetch will result in swell and moderate seas through the period.
This will keep the Bay and Gulf conditions under SCA levels, but 
some periodic SCEC conditions cannot be ruled out. Isolated to 
scattered marine showers and thunderstorms will be possible for
much of the period. Any heavier cells could result in locally 
gusty winds and higher seas. 




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