Rosa, a hurricane that was downgraded to a tropical storm and then to a tropical depression, reportedly killed one person in northwestern Mexico before moving north into the U.S.
The National Weather Service issued a flash flood warning for the Phoenix area, saying that more than 2 inches (5 centimeters) of rain fell in metro Phoenix by midmorning and additional rain was expected. The day has already made it one of the wettest Octobers Phoenix has seen, the agency said.
The city sees sudden and heavy downpours during the summertime monsoon, but the continuously falling rain is a rarity.
The heavy showers caused a riverbed to overflow, spilling muddy waters into a north Phoenix intersection. Firefighters slogged through waist-deep water to get to people stuck in their cars. Crews pulled at least six people, including a child, from vehicles and carried them one at a time to a firetruck.
Around 10 vehicles, including a bus, were either at a standstill in the water or tried to drive through it.
The wet weather was a factor in numerous Phoenix-area freeway wrecks but no serious crashes were reported, said Trooper Kameron Lee of the Arizona Department of Public Safety.
Authorities warned drivers to avoid entering streets or washes inundated with water.
A reporter for Phoenix news station KNXV-TV posted a video on social media showing a person riding a unicycle into a flooded area, prompting the weather service to reiterate that all types of vehicles should stay away.
The rain also led three elementary schools and one high school to close for the day. Maricopa Community Colleges canceled classes at all 10 of its campuses.
Flash flood watches were in effect in parts of Arizona, California, Nevada and Utah. Utah Gov. Gary Herbert mobilized about 200 National Guard soldiers Monday to prepare for potential flooding south of Salt Lake City.
The soldiers planned to build flood berms and erect barriers and sandbags, officials said.
In parts of southern Arizona, a flood warning was in effect until midafternoon. Heavy rain Monday flooded streets in the city of Yuma at the U.S.-Mexico border and caused power outages. At least six roads in Tucson were closed because of flash flooding.
Mexican authorities had declared a state of emergency for Ensenada, on Baja California state’s Pacific coast, and Mexicali, the state capital across the border from Calexico, California. Mexican media outlets reported that a woman was swept away by floodwaters and drowned in the city of Caborca, Sonora, on the Sea of Cortez.
Meanwhile, a separate storm, Hurricane Sergio, grew to major hurricane status in the Pacific on Tuesday, though it posed no immediate threat to land. It has sustained winds of 115 mph (185 kph), making it a Category 3 storm, U.S. National Hurricane Center said.
It’s centered about 870 miles (1,400 kilometers) south-southwest of the southern tip of the Baja California Peninsula and has been heading west at 13 mph (20 kph). Forecasters say they expect it to keep moving out to sea.
Associated Press writer Paul Davenport contributed from Phoenix.