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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 171948 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Brownsville TX
248 PM CDT Mon Jun 17 2019

.SHORT TERM (Now through Tuesday Night): Showers and 
thunderstorms were triggered along an outflow boundary this 
morning, which had originated from a complex of storms moving down
the Texas coast. Pockets of 1-1.5" rain amounts are estimated to 
have fallen (per the radar) mainly over Cameron, Willacy, Kenedy, 
and eastern Hidalgo counties. Activity waned quickly around 
noontime, with only a few dissipating showers left over Kenedy 
County at this time. Mid/upper- level short-wave ridging, with 
axis now over west Texas, is moving in now, and will preclude 
mentionable precip (at least over land) for the rest of the short-
term period.

Temperatures for this afternoon a bit tricky; had adjusted down a
few degrees earlier with outflow originating over the Gulf 
overspreading much of the area. However, BRO has recovered to 93F,
with heat index values reaching 108-109F. From tonight on, 
though, temp forecast appears to be more straightforward: Upper 
70s are forecast for lows tonight, with the populated RGV and 
coastal areas hanging near 80. With light SE winds expected 
tonight, could see a few areas of shallow "mist" where ground 
manages to stay wet through this afternoon, but not expecting this
to be too much of an issue.

For tomorrow, with upper ridging continuing to build in from the 
west, H85 temps and 1000-500mb thicknesses nudging up as well, so 
it will be hot. Going with 94/97/99F for BRO/HRL/MFE, 
respectively, with temps of 104-105 near Falcon Dam and Zapata. 
These are actually only 2-3 degrees above climo (but it is mid- 
June, after all!). Made some tweaks to dewpoint fields, yielding 
heat index values of 108-112F for a couple of hours tomorrow 
afternoon. Successive shifts will have to monitor for a possible 
Heat Advisory; not quite confident enough on duration (2+ hours of
111+ heat indices) at this juncture. With light flow in place, a 
sea-breeze is likely to develop, which may take the edge off the 
heat slightly as it moves inland during the afternoon. Atmospheric
moisture will likely be too shallow for it to trigger any 
showers, though.

Yet another warm, muggy night follows Tuesday night. As a surface
low moves into the Southern Plains, winds not expected to be 
quite as light locally. Expecting temps along the Rio Grande to 
only dip to 80-82F.

.LONG TERM (Wednesday through Monday): Hot and humid weather with
above average temperatures will prevail as a 500 mb ridge remains
stolid over northern Mexico. Surface high pressure across the 
Gulf of Mexico will result in onshore breezes and limited moisture
moving up from the south. Rain chances will remain limited across
deep South Texas and the RGV through the weekend. Southeast to 
south winds will strengthen a bit Wednesday through Monday as a 
series of surface low pressure systems develop and move across 
the Plains, producing a tighter gradient. Breezy to windy 
conditions will be possible across the area by late in the week. 
Afternoon high temperatures will range from near 90 at the 
immediate coast, to several degrees above the century mark inland 
west, a few to several degrees above normal. Heat index values of 
105 to 110 degrees will be quite typical in the late morning and 
early evening, with peak values from 111 to 115 degrees for a few 
hours each afternoon. A few readings will likely hit 116 degrees 
or better late in the week and into the weekend. Afternoon heat 
advisory conditions will be common. Low temperatures will range 
from the middle 70s to lower 80s, also a few to several several 
degrees above normal. The ridge will shift slightly east Friday 
through Sunday as deeper troughing develops over the western 
United States. This may provide an opening for a few showers to 
move up the coast, and for convection to develop over the Sierra 
Madre Oriental range and the Big Bend Saturday night. With a 
general consensus among the models this run, used a blend as a 
basis for the forecast with above average confidence.


Now through Tuesday Night: Boating conditions should continue to
improve overnight as pressure gradient slackens, leading to
moderate SSE winds of 10-12 knots, and any residual agitated seas
from this morning's convection settle down. SE winds continue at
10- 15 knots across the coastal waters Tuesday and Tuesday night,
with relaxed seas around 3 ft.

Wednesday through Saturday night: High pressure will remain 
ensconced across much of the Gulf in the long term. Transient low 
pressure systems in the Plains will tend to tighten the gradient 
for the second half of the week. Moderate southeast to south winds
and moderate seas will increase Wednesday night through Saturday 
night. Winds will increase to 15 to 20 knots, meaning small craft 
should exercise caution. Wave heights will also trend upward, with
low end small craft advisory conditions possible on the Gulf 
waters from Thursday night through Saturday night.


BAYVIEW/PORT ISABEL  80  92  80  93 /  10  10   0   0 
BROWNSVILLE          80  95  81  96 /  10  10   0   0 
HARLINGEN            79  97  79  98 /  10  10   0   0 
MCALLEN              79  99  80 102 /  10  10   0   0 
RIO GRANDE CITY      78 102  80 106 /  10  10   0   0 
SOUTH PADRE ISLAND   82  86  82  87 /  10  10   0   0 




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