Tropical Storm Rosa nears Mexico's Baja California coast

In this Sunday, Sept. 30, 2018 photo, a vehicle drives east on a flooded street following a rain storm, in Yuma, Ariz. Tropical Storm Rosa neared Mexico's Baja California on Monday, spreading heavy rains that were projected to extend into a drenching of the U.S. Southwest. (Randy Hoeft /The Yuma Sun via AP)

MEXICO CITY -- Tropical Storm Rosa soaked northwestern Mexico with heavy rains as it neared the Baja California Peninsula late Monday, reportedly claiming at least one victim, and was projected to extend into a drenching of the U.S. Southwest.

The U.S. National Hurricane Center said Rosa should move over Baja California and Sonora, weakening and bringing 3 to 6 inches (7.5 to 15 centimetres) of rain, with its remnants expected hitting the southwestern United States on Tuesday.

It's forecast to bring 2 to 4 inches (5-10 centimetres) of rain to central and southern Arizona and 1 to 2 inches (2.5-5 centimetres) to the rest of the desert Southwest, Central Rockies and Great Basin. Some isolated areas might see even more precipitation.

Rosa's maximum sustained winds had decreased to 40 mph (65 kph) as of Monday night, and the storm's centre was about 75 miles (125 kilometres) north of Punta Eugenia in Mexico. It was heading northeast at 10 mph (17 kph).

The Civil Defence agency for Baja California state said schools would be closed Monday in several communities, including the state capital of Mexicali, across the border from Calexico, California; San Felipe, on the northern Sea of Cortez; and south of Ensenada, on the peninsula's Pacific coast.

Federal authorities declared a state of emergency for Ensenada and Mexicali.

Classes were also suspended in communities in Sonora, where Civil Defence officials advised people to avoid driving on the coastal highway. The agency posted video online of floodwaters racing through an arroyo and covering a stretch of road, carrying trees and logs in the current.

Various 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.

The National Weather Service earlier announced flash flood watches through Wednesday for areas including southern Nevada, southeastern California, southwestern and central Utah and the western two-thirds of Arizona.

Forecasts call for heavy rainfall in the watch areas, which include Las Vegas, Phoenix and Salt Lake City, with possible flooding in slot canyons and normally dry washes and a potential for landslides and debris flows from recent wildfire burn scars.

National Weather Service meteorologists in Phoenix said central and northern Arizona stood to get hit with the heaviest amounts of precipitation.

Metropolitan Phoenix, where temperatures were above 100 degrees Fahrenheit (38 Celsius) only a few days ago, had already cooled to the 80s thanks to Rosa. Moisture associated with the storm arrived ahead of it, bringing rain Sunday night and Monday morning. Phoenix meteorologist Jaret Rogers said more showers were expected across central Arizona later in the day before a weakened Rosa arrives in the area Tuesday morning.

According to the National Weather Service, the entire Phoenix area is expected to see between 1 and 2 inches (2.5-5 centimetres) of rain. But some areas could see between 2 to 3 inches (5 to 7.5 centimetres).

"All that means is conditions are favourable for flash flooding if it rains," Rogers said. "It doesn't mean something's imminent."

Several cities posted on social media that they were distributing sandbags.

Meanwhile, Tropical Storm Sergio became a hurricane in the Pacific, though it posed no immediate threat to land.

Sergio had winds of 75 mph (120 kph) and was centred about 760 miles (1,220 kilometres) southwest of Manzanillo, Mexico. The storm was moving west at 14 mph (22 kph).

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Associated Press writer Peter Orsi reported from Mexico City, and Terry Tang reported from Phoenix.