Life-threatening flash flooding is possible across the desert Southwest in the coming days as moisture from the remnants of Tropical Storm Polo streams into the region, forecasters warned.
The National Weather Service said heavy rainfall could dump several inches of water on parched terrain from Arizona into New Mexico and West Texas, raising the risk of sudden, fast-moving floods in canyons, washes and low-lying communities.
Polo weakened after churning off Mexico's Pacific coast, but its leftover moisture is being pulled north by a monsoon pattern already parked over the Southwest. That combination is what worries meteorologists.
"The ground is hard and dry in a lot of these areas, so it can't absorb rain fast enough," said one NWS forecaster briefing local emergency managers. "That water runs off and it runs off fast."
Flash flood watches were expected to expand across the region as the storm's moisture arrives. Cities including Phoenix, Tucson, Albuquerque and El Paso could see rounds of intense thunderstorms, with the heaviest activity forecast overnight and into the early morning hours, when flooding is hardest to see.
The danger is not limited to urban areas. Slot canyons, burn scars from recent wildfires and desert roads that cross normally dry riverbeds are especially vulnerable. A wall of water can sweep through a wash within minutes of rain falling miles away.
Officials urged residents and travelers to avoid driving through flooded roadways, a leading cause of flood deaths in the Southwest. "Turn around, don't drown" remains the standard warning from the National Weather Service, which notes that just a foot of moving water can float most vehicles.
The Southwest is no stranger to this kind of threat. Monsoon season each summer funnels tropical moisture into the region, and remnant storms from the Pacific have produced deadly floods before. In 2018, remnants of Hurricane Rosa triggered flooding across Arizona. Similar setups have washed out roads and stranded hikers in Utah and New Mexico.
Emergency crews in several counties said they were staging high-water rescue teams and monitoring low-water crossings. Residents in flood-prone areas were told to keep phones charged and be ready to move to higher ground on short notice.
The rain is also a mixed blessing. Much of the Southwest is locked in long-term drought, and the moisture could ease dry conditions in some areas. But forecasters cautioned that the risk of flash flooding outweighs any short-term benefit when rain falls this hard and this fast.
Officials said conditions could change quickly and urged residents to monitor local forecasts and wireless emergency alerts through the weekend.
