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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 182118

Area Forecast Discussion
National Weather Service Brownsville TX
418 PM CDT Wed Sep 18 2019

.SHORT TERM (Now through Thursday Night): As the 500 mb closed low 
associated with the remnants of TS Imelda continue moving slowly 
northwards, 500 mb ridging will steadily build over the RGV 
resulting in a gradually stabilizing atms. The 12Z BRO sounding 
still shows some decent tropical moisture in place across the 
region. This lingering moisture may combine with the usual afternoon 
heating tomorrow to allow for some isold afternoon conv. Also isold 
marine conv can not be ruled out mainly during the overnight and 
early morning hours. So will maintain some slgt chc pops throughout 
the short range period. 

The increasing 500 mb ridging will allow for steadily warming temps 
tomorrow. The current temps across the western counties have topped 
out near the century mark today. Expect high temps tomorrow to be 
near or exceeding highs today especially out west. Will be going 
near 103 for Zapata Co with mid 90s likely across the coastal 
counties. The short term numerical guidance from the NAM/GFS and 
ECMWF models are in pretty good agreement through Thurs Night and 
will lean closer to a NAM/ECMWF blend as the GFS seems to be a 
bit too cool for highs. 

The heat index values for tomorrow afternoon will be quite high and 
may briefly touch up close to Heat Advisory levels. For now will 
hold off on issuing any Advisory as the indices may not be long 
enough in duration to meet Advisory criteria. 

Will also mention some potential for patchy fog across our northern 
counties tonight as the fairly light surface winds across the 
northern Ranchlands combine up with the pretty elevated low level 

Overall confidence in the short range forecast is above average 
today due to the pretty decent model agreement.

.LONG TERM (Friday through Wednesday): As the remnants of Imelda 
lift north and eastward into the Plains and Midwest US, an 
elongated, high pressure ridge will build over the Gulf 
Coast/Southeast US. Flow around the ridge will keep Gulf moisture 
advecting over Deep South Texas through at least the upcoming 
weekend. Global models keep PWATs around or just slightly below 
2.00 inches through Monday. This will likely result in isolated to
scattered convection along the late morning/afternoon sea breeze 
each day. 

Long-range forecast models begin to diverge by Monday, with the
12z GFS showing a potent, aggressive short-wave trough/cut-off 
low, quickly digging into Northern Texas from the Pac NW by 
Tuesday afternoon. The associated surface low brings in a weak 
cold front or a pre-frontal trough into the northern CWFA late 
Wednesday night, into Thursday. Meanwhile, the 12z ECMWF also has 
a short-wave trough/cut-off low developing over the Pac NW, but 
has it digging over Southern California Tuesday afternoon, with 
mid-level riding building over Texas. Will lean more toward the 
persistent, drier and warmer ECWMF solution for now.
Temperatures are expected to remain generally the same each day in
the long term, give or take a degree or two. High temperatures 
will be about 3 to 6 degrees above seasonal average -- mainly in 
the mid-upper 90s to near 100 degrees out west. Lows will be 
about 5 to 10 degrees above normal -- generally in the mid-upper 
70s each night to near 80 degrees near the coast. 


.MARINE (Now through Thursday Night): The broad surface ridging 
centered over the SE U.S. will be strong enough to keep the Bay and 
Gulf conditions close to SCEC conditions throughout the short term 
period. But at this time, an extended period of SCA conditions is 
not expected for the lower TX coastline.

Friday through Wednesday: Swell approaching the Lower Texas Coast
may produce Small Craft Exercise Caution for a portion of the 
Gulf of Mexico waters from Friday night through Sunday night. A 
slight lull in swell and seas is expected Monday through Tuesday 
morning before increasing again to around 4 to 5 feet Tuesday 
afternoon and evening, especially for the offshore coastal waters.
Winds are anticpated to be moderate, occasionally gusty, out of 
the southeast or south-southeast through the long-term period. 


BAYVIEW/PORT ISABEL  79  91  78  92 /  10  10  10  20 
BROWNSVILLE          80  95  80  94 /  10  10  10  20 
HARLINGEN            78  95  77  96 /  10  10  10  20 
MCALLEN              79  99  78  99 /   0  10   0  20 
RIO GRANDE CITY      77 100  78  98 /   0   0   0  10 
SOUTH PADRE ISLAND   82  87  82  88 /  10  10  20  20 




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Short Term...60 
Long Term/Upper Air...67