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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 181957

Area Forecast Discussion
National Weather Service Brownsville TX
257 PM CDT Sun Aug 18 2019

.SHORT TERM (Now through Monday night): Heat index values have 
reached 112 degrees in Brownsville and 111 degrees in McAllen this 
afternoon with temperatures currently near 100 to 103 degrees. Will 
continue heat advisory for now as temperatures will be hot for the 
next couple of hours and whether the heat index is 110 or 111 
degrees...the impacts from the heat will continue through the rest 
of the afternoon into the early evening hours. 500mb subtropical 
ridge entrenched across west Texas and northeast Mexico will 
continue to provide strong subsidence across southwest Texas tonight 
into Monday. Low to mid level moisture is expected to be higher 
across portions of the northern and western Gulf of Mexico tonight 
into Monday but moisture will continue to be limited across the CWA 
through Mon night. With that rain chances are expected in 
the short term and temperatures will remain above normal Monday but 
should remain below record high temperatures Mon afternoon. Heat 
advisories will likely be needed for the eastern portions of the CWA 
Mon afternoon though. 

.LONG TERM (Tuesday through Sunday): Mid level ridging over  
northwest Texas will continue to provide subsidence across south 
Texas through Tuesday. The 500mb ridge will then move westward 
into the Four Corners region Mid to late week. Low to mid level 
moisture is expected to increase across portions of the western 
Gulf of Mexico Wednesday into Thursday as a 500mb low/inverted 
trough moves across the southwest Gulf of Mexico Thursday. This
feature will support a slight chance to chance of showers and
thunderstorms, mainly along the coast and across the Gulf waters, 
Wednesday into Thursday. The increase in cloud cover and rain
chances should keep high temperatures a bit lower through mid to
late week. 

The rest of the forecast period is dependent on the development 
of a closed 500mb low across the northwest Gulf of Mexico by late
in the week. The ECMWF continues to indicate that this feature 
move along the northwestern Gulf of Mexico on Friday with most of
the moisture remaining offshore. However, the GFS shows a weaker
and wetter system moving across the northwestern Gulf. No
significant changes were made to the previous pop grids forecast.
Will keep the mention of a slight chance of showers and 
thunderstorms across the CWA through the rest of the week into 
the weekend with more robust rain chances offshore.


.MARINE (Tonight through Monday night): Seas were near 4.6 feet 
with south to southeast winds near 11.7 knots at buoy020 early 
this afternoon. Moderate to strong southeast winds will prevail 
across the coastal waters tonight with surface low pressure across
west Texas and high pressure across the eastern Gulf of Mexico. 
Will word SCEC for the Laguna Madre this evening and for the 
offshore waters tonight. The pressure gradient will weaken 
slightly across the western Gulf of Mexico Monday. Light to 
moderate southeast winds will prevail across the offshore waters 
Monday into Mon night with stronger winds across the Laguna Madre 
providing SCEC conditions across the bay waters Mon afternoon. 

Tuesday through Thursday Night...Light to moderate southeast 
winds will continue across the coastal waters on Tuesday and 
Tuesday night with surface high pressure across the eastern Gulf 
of Mexico. The pressure gradient will begin to weaken by midweek 
and allow winds to diminish on Wednesday. Light southeast winds 
should prevail across the western Gulf of Mexico Wednesday into 
Thursday. Showers and thunderstorms will be possible at times 
across the coastal waters through the period.


.FIRE WEATHER...Relative humidity values will be slightly higher 
across the western portions of the CWA Monday but 20ft winds will 
increase to 15 to 20 knots across the Rio Grande Valley Mon 
afternoon. The fire danger is currently high across the area with 
very high readings across the western portions of the CWA. Fuel 
dryness is currently critically dry across most of deep south 
Texas with extremely dry fuels across southern portions of Hidalgo
County. Will likely need a fire danger statement for the Rio 
Grande Valley and northern ranchlands Monday afternoon except 
across the coastal counties of deep south Texas where relative 
humidity levels should remain above 40 percent. 


BAYVIEW/PORT ISABEL  82  97  80  93 /  10  10  10  10 
BROWNSVILLE          82  98  79  95 /  10  10  10  10 
HARLINGEN            80 100  78  98 /  10  10  10  10 
MCALLEN              82 102  80 100 /  10  10  10  10 
RIO GRANDE CITY      80 104  79 102 /  10  10  10  10 
SOUTH PADRE ISLAND   83  92  82  86 /  10  10  10  10 


TX...Heat Advisory until 6 PM CDT this evening for TXZ250>257-351-353.



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