Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 191120
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
620 AM CDT Mon Jun 19 2017

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

&&

.AVIATION...VFR conditions to prevail through the period. Not as
breezy today across Deep South Texas compared to Sunday as
surface high pressure is now spread across central TX leading to a
slackened pressure gradient. May see some east or southeast gusts
to around 16 knots this afternoon before winds begin to diminish
with the setting sun.

&&

.PREV DISCUSSION... /issued 414 AM CDT Mon Jun 19 2017/

SHORT TERM (Today through Tuesday): A strong upper ridge
centered over the southwest U.S. will maintain a dry northeast
flow aloft over Deep South Texas today with easterly onshore flow
at the surface. Main forecast issue again today will be the
impacts from high heat and humidity. Will issue a Special Weather
Statement to highlight heat index values in the 103 to 108 degree
range. Basically the same story for Tuesday, and while low level
moisture will increase slightly overnight tonight into Tuesday,
heat index values will mostly be a repeat Tuesday afternoon from
this afternoon. It will not be as breezy today compared to Sunday
as the surface pressure gradient has relaxed in response to
surface high pressure building over central/east TX. Will see
little change in the pressure gradient on Tuesday for a
continuation of modest winds. Precipitation free conditions to
prevail for the land areas through the period despite the
likelihood of a tropical low impacting the west central Gulf
Tuesday.

LONG TERM (Tuesday Night through Sunday): Uncertainty continues
to plague the long term period as medium-range model solutions to
the potential tropical system remain rather diverse this morning.
That being said, models do have some overall agreement with the
general pattern aloft. Strong subtropical 500mb ridging will
continue across the Desert Southwest with troughing over the
Great Lakes region and portions of the Northeast. There is a
quasi-stationary front that is slowly drifting south through the
Southern Plains that will generally stall near the the Northern
Gulf of Mexico coastline. Meanwhile, the Bermuda High stays
located east of the Florida Peninsula. The GFS continues to
develop a low in the Gulf over the next few days which moves north
towards the stalled front and generally becomes wrapped into that
system. Meanwhile, the ECMWF/Canadian/NAM, all having varying
solutions that meander the low west and then northwest across the
Gulf. Although the EURO still brings the system closest to the
RGV, it is interesting to note that the majority of the moisture
and precip associated with is stays on the eastern side closer to
the trough axis and frontal boundary.

But, given that the low pressure area of interest is still
located on the eastern side of the Yucatan Peninsula, has no
distinct center of circulation, and has yet to emerge into the
southern/central Gulf, it is difficult to refine any details of
the forecast through the week. As such, have left much of the
forecast as status quo for now, with minor changes to the precip
coverage. It appears that there could be some slight chance to
chance POPs for the coastal counties and possibly into portions of
the Mid Valley by Tuesday night and Thursday time frame. By late
Thursday into Friday, most model solutions do have the system
either already north or else moving north across the
Western/Northern Gulf anywhere along the Northeastern Texas to
Louisiana coastlines.

While the bulk of the moisture does appear to remain away from
Deep South Texas with this system, it doesn`t mean our chances for
precip are zero. The long-range models do indicate another surge
of moisture and perhaps an inverted trough that will keep rain
chances, albeit small ones, in the forecast through the weekend.
Regardless, the subtropical ridge will still dominate the
Southwestern U.S. and Texas with hot temperatures through much of
the week. Values are expected to lower a bit by the weekend,
should the rain pan out.

MARINE:

Today through Tuesday: Modest seas and east winds to prevail
across the waters today/tonight as surface high pressure over the
northwest Gulf has shifted inland over Texas. A weakness over the
west central Gulf in the form of low pressure aloft looks to
deepen on Tuesday sending higher swells westward into the Gulf
waters of the lower Texas coast. A Small Craft Advisory may be
needed for the outer Gulf waters Tuesday afternoon.

Tuesday Night Through Friday: Much uncertainty remains this
morning with regard to the potential development of a tropical
system Tuesday through Thursday. As of now, showers and
thunderstorm potential will be highest of the offshore waters
through the period as the surface low tracks across portions of
the Central to Western Gulf. Seas will continue to run high on
Tuesday night into Wednesday as swells remain elevated. Small
craft advisories may continue for a time. Sea should begin to
improve late Wednesday with more moderate seas returning as the
prevailing summer-time pattern returns. However, the surface
pressure gradient will begin to strengthen late in the week with
winds and seas slowly increasing.

&&

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

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

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