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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 202023

Area Forecast Discussion
National Weather Service Brownsville TX
323 PM CDT Mon May 20 2019

.SHORT TERM (Now through Tuesday night): A rigorous 500mb low 
pressure system will track eastward across the Central Plains with
a lee surface low expected to deepen in the next 24 hours. This 
combined with a surface high across the Northeast Gulf of Mexico 
will result in strong southeasterly winds across Deep South Texas 
through the afternoon with a few strong wind gusts continuing into
the overnight hours. Held off on a Wind Advisory for now with
time-heights indicating 35 to 40 knots at 2000 to 4000 feet AGL,
which may not be enough to mix down for frequent 40 mph gusts. 
Will have to keep an eye out if the low-level jet can strengthen 
and mix down stronger winds later tonight. 

Tonight, winds will remain elevated as the surface low continues
to deepen. Overnight low temperatures were bumped up justifiably
from the last shift due to warm dew points and elevated surface
winds, so have left those as-is. It will be quite the muggy
evening tonight. Temperatures on Tuesday will be hot and humid
once again with Heat Indices of 100 to 105F, so we urge those
spending time outdoors to take frequent breaks. Model time-
heights indicate RH values of 25% or lower up to 850mb, so rain 
chances will be near zero, as warm, subsident air continues to
flow into the region.

.LONG TERM (Wednesday through Monday): At the beginning of the 
long term a large upper low pressure trough will dominate the 
CONUS from the Midwest to California while mid/upper level ridge 
extends from the Mid- Atlantic/SE States into the Western Gulf of 
Mexico. This anomalous trough/ridge pattern retrogrades slowly 
westward with the center of the ridge settling near the mouth of 
the Mississippi while the trough axis becomes more aligned over 
the West Coast states and Inter-mountain West the coming weekend 
and early next week. 

Deep South Texas will remain on the western periphery of the high 
pressure ridge with the Upper trough/low remaining well to the 
northwest of the region to have any significant impacts. 12Z model 
suite continues to show good agreement and consistency with this 
pattern with only some slight differences in exact placements of the 
center axis of both the trough and ridge by the end of Long term. 
Overall, no significant changes to the forecast grids at this time. 
Model guidance is trending a few degrees lower as we approach the 
latter half of week, but with the center of the ridge edging 
westward I do not foresee any potential drop and on the contrary 
would except some areas to see potentially warmer temperatures. In 
any case, the general weather pattern and forecast to remain 
unchanged through the remainder of the week. The atmosphere stays 
rather dry with subsidence from the ridge keeping the CWA rain free. 
Heat and humidity to combine maintaining elevated temperatures and 
heat indices and the pressure gradient shows no signs of weakening. 
This spells out to 90-100+ degrees for day time highs, overnight 
lows 75-82, heat indices 100-109 (at least) and winds 15-30 mph and 
we are one month away from the official start of Summer.


.MARINE (Now through Tuesday night): Dangerous marine conditions
are expected this afternoon through the overnight hours as
southeasterly winds strengthen and seas quickly build to hazardous
levels. Small Craft Advisories are in effect for all lower Texas
coastal waters now with Gale conditions expected for the Gulf
waters as early as 7 PM this evening. Therefore, have upgraded the
Gale Watch to a Warning, which will continue until 7 AM. Tuesday
afternoon the gradient should relax, but seas will be slower to

Wednesday through Saturday: The weather pattern across the 
Western Gulf to remain stagnant with the pressure gradient remaining 
steady state.  Low pressure to the west and high pressure over the 
Gulf will continue to provide a strong onshore flow which will 
result in  continuation of adverse marine conditions much of the 
week. Frequent and possibly continuous (for the Gulf waters) Small 
Craft Advisories are likely through Friday and may linger into next 


BAYVIEW/PORT ISABEL  80  90  79  89 /  10  10  10   0 
BROWNSVILLE          80  96  80  95 /  10  10  10   0 
HARLINGEN            80  97  79  96 /  10  10  10   0 
MCALLEN              80 100  79  98 /  10  10  10   0 
RIO GRANDE CITY      79 101  78  99 /  10  10  10   0 
SOUTH PADRE ISLAND   80  84  79  84 /  10  10  10   0 


GM...Small Craft Advisory for winds until 7 AM CDT Tuesday for GMZ130-

     Small Craft Advisory until 10 PM CDT this evening for GMZ150-155-

     Gale Warning from 10 PM this evening to 7 AM CDT Tuesday for 



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Short Term...65 
Long Term...59