Heavy rains starting Saturday evening were expected to bring a threat of flash flooding to already saturated areas of the U.S. Southwest through Monday, according to the National Weather Service.

As much as 4 inches (10 centimeters) of rain could fall across the region, where a number of weather systems have brought a deadly autumn of soaking rains. In the Phoenix area on Friday evening, emergency crews rescued people from several vehicles on flooded streets.

“It’s not going to take much rainfall to be impactful at all in some of these locations just because of how saturated they are,” said Allison Santorelli, a meteorologist with the Weather Prediction Center in College Park, Maryland.

The National Weather Service has issued flood watches for nearly all of Arizona and parts of southern Utah, southwestern Colorado, and western New Mexico, in addition to part of southern Nevada. Those watches include the Four Corners region, a sparsely populated area where Arizona, Colorado, New Mexico and Utah meet that has been hit especially hard by recent rains.

Santorelli said this weekend's rain was expected to bring both flash flooding and small-stream river flooding.

The Phoenix Fire Department said in a post on X that it rescued people from four vehicles on flooded streets on Friday night, while a fire captain in nearby Scottsdale said on Facebook crews were rescuing a person in one vehicle on a flooded street when another vehicle carrying two people drove into the same waters and had to be rescued.

Scottsdale fire Capt. Dave Folio said in a video posted on Facebook that just 2 inches (5 centimeters) of water can "sweep your vehicle off its wheels,'' and that the vehicles were in 3 to 4 feet (0.9 to 1.2 meters) of water.

In Bullhead City, Arizona, located on the state's border with California, heavy rains on Friday left water, rocks and debris on streets across the city and closed parks, the city said in Facebook posts.