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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 252048

Area Forecast Discussion
National Weather Service Brownsville TX
348 PM CDT Fri May 25 2018

.SHORT TERM (Tonight through Saturday Night): Another hot day 
across deep south Texas and the RGV today. Only difference from 
yesterday is a bit drier air aloft and very little in the way of 
sea breeze convection. As of writing this discussion, the sea 
breeze had pushed into central Cameron/Willacy/Kenedy Counties. 
Temperatures here at KBRO have dropped a few degrees over the past
hour (was 96F now 93F).

A very tranquil weather pattern has set up for the region and should 
continue into much of the short term period. Dry northwesterly flow 
will continue to keep rain chances between 0-10 percent and the 
upper ridge just upstream will be close enough to help our daily max 
temps hit near 100 degrees for much of the region with the exception 
of along and east of the I69E corridor. Overall a very hot and dry 
start to the Memorial Day weekend is expected.

.LONG TERM (Sunday through Friday): The overall synoptic pattern
over the lower 48 states will be dominated initially by a large
500 mb closed low centered over the western States with the large
500 mb circulation associated with Alberto as the storm moves
closer to the central and eastern Gulf Coast. As both of these
circulations lift off to the north and northeast later next week
and additional 500 mb troughs push into the West Coast, 500 mb
ridging will build steadily over Mexico and southern TX. This will
result in steadily warming temps and decreasing overall moisture
and instability levels. So will be going with near zero pops
throughout Day 7 with overall temps well above climo for late
May. The combination of the surface dewpoints and the increasing
afternoon temps will also likely result in heat index values 
reaching up into the 105 to 110 range in many sections of the RGV 
for next week. 

Longer range tropical numerical guidance keeps Alberto moving in a
general N-NW direction throughout the holiday break which will
keep the system confined to the eastern half of the Gulf of Mex.
This will keep the RGV and Deep South TX well west of any of the
outermost rain bands associated with the storm. However, if
Alberto develops a large enough wind/swell field, some larger 
swell activity could increase along the lower TX coastline 
possibly enhancing the rip current risk a bit. This will depend 
highly on the overall track and level of development of Alberto 
before moving inland. 

The only bit of potential relief from the heat in the longer 
range period will be the possible approach of an inverted 500 mb 
trough axis moving west into the SW Gulf of Mex under the 
persistent ridge axis by next weekend. The big question will be 
how much impact on temps/pops will this feature have on the RGV 
late in the forecast period. Until then increasing heat will 

Overall agreement in the 500 mb pattern over the lower 48 states
is pretty high between the GFS and ECMWF. Both models maintain the
very strong ridge axis over the RGV through Day 7. Run to run 
consistency with both longer range models is pretty stable also. 
So overall confidence in the longer range forecast wording is 
above average. Will go close to model consensus for min temps 
through Day 7 and will go slightly warmer that model blends for 
afternoon high temps as the blends may be underestimating the 
warmup just a bit. 


.MARINE (Tonight through Saturday Night): Light winds and seas to 
start the short term marine period. Not much change is anticipated 
as winds should remain around or less than 10kts for the Laguna/Gulf 
waters. There will probably be a subtle increase in wave heights 
toward the end of the cycle as Subtropical Storm Alberto moves 
northward from the Yucatan and into the central and eastern Gulf 
(well east of our vicinity). It's difficult to say exactly how much 
this will increase swells, however, given overall weak nature 
(current and forecast) did take a fairly conservative approach to 
wave heights toward the end of this forecast period.

Sunday through Wednesday Night: The surface circulation associated
with Alberto will likely remain located too far east to have much
of an impact on the surface winds along the lower TX coastline.
This will allow light to moderate S-SE low level flow to prevail
over the region. This will likely keep the overall swells below
SCA level. So no SCA conditions expected through next Wed. 


BAYVIEW/PORT ISABEL  75  91  73  93 /   0   0   0   0 
BROWNSVILLE          74  95  74  98 /   0   0   0   0 
HARLINGEN            73  97  73 100 /   0   0   0   0 
MCALLEN              74  99  74 103 /   0   0   0   0 
RIO GRANDE CITY      74 101  73 104 /   0   0   0   0 
SOUTH PADRE ISLAND   76  84  77  86 /   0   0  10   0 




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Long Term...60