The National Weather Service issued a massive flood watch across Central and South Texas early Thursday, May 21, 2026, warning that heavy holiday weekend rainfall could trigger life-threatening flash floods through Monday.
Atmospheric conditions are being fueled by increasing tropical forcing from the Madden-Julian Oscillation and a negative Southern Oscillation Index, signaling an emerging El Nino climate.
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Forecasters predict widespread rainfall totals of 2 to 4 inches, with isolated areas receiving up to 6 inches, while regions in East Texas could see over 7 inches.
Flood Risks and Urban Impacts
Saturated soils from previous storms have significantly lowered flash flood guidance across South Texas, leaving some eastern sections vulnerable to flooding from less than half an inch of rain within three hours.
The weather service urged residents in flood-prone areas to monitor forecasts closely and prepare for sudden disruptions.
"There is a potential for life-threatening flooding somewhere in the watch area," the weather service said.
"Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations."
The agency also detailed specific risks facing urban communities as consecutive rounds of thunderstorms move through the region over the weekend.
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"Flooding caused by excessive rainfall is possible," the NWS stated. "Excessive runoff may result in flooding of rivers, creeks, streams and other low-lying and flood-prone locations.
Creeks and streams may rise out of their banks. Flooding may occur in poor drainage and urban areas."
Meteorologists emphasized that a watch means conditions are favorable for flooding, whereas a warning indicates that flooding is imminent or already occurring.
"With the expectation of more rain this week and into the weekend, flooding will be possible, especially within the strongest thunderstorms," the NWS said.
The multi-regional advisory covers Austin, San Antonio, Laredo, Corpus Christi, and the entire Rio Grande Valley.
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Heavy rainfall early Thursday has already caused street flooding in Weslaco, prompting road closures, Valley Metro transit delays, and 277 power outages reported by local utility cooperatives.
