California [US], August 21: The US state of California is bracing itself for tropical storm Hilary, which is already bringing fierce winds and flooding to Mexico's Pacific coast.
It is lashing the Mexican state of Baja California with winds of 70 mph (119km/h). One man died there trying to cross a stream in his car.
A number of houses are now submerged in the town of Santa Rosalia.
Hilary is predicted to weaken as it moves north and should reach California on Sunday afternoon local time.
It would be the state's first tropical storm in 84 years.
The last time a tropical storm made landfall in southern California was in Long Beach in 1939.
Experts say recent abnormal weather events that have plagued the US - and several areas across the globe - have been influenced by human-caused climate change.
The storm made landfall in the northern part of Mexico's Baja California peninsula at 11:00 local time (18:00 GMT) on Sunday, the US National Hurricane Center (NHC) said.
It warned that Hilary could cause "life-threatening" floods in both Mexico and the US.
In Mexico, 18,000 soldiers were placed on standby earlier to assist in rescue efforts.
The man who died in Baja California was in a car with his wife and children, local officials said - his family survived.
In Santa Rosalia, on the eastern coast of Baja California, dramatic videos have emerged showing powerful torrents of muddy water cascading down the main street.
Across California, residents have been putting out sandbags, including in Long Beach and Palm Springs.
Eugenie Adler, a resident of Long Beach, told Reuters: "Flooding where people lose some property is one thing, but flooding where people die is another. And I'm afraid people might die."
Los Angeles mayor Karen Bass called it "an unprecedented weather event".
"But Los Angeles has deep experience responding to crises whether it be wildfire or earthquakes," she said. "The city is prepared."
Nearly 26 million people in the southwestern US are under flood watch.
Hilary was downgraded to a Category 1 storm after weakening on Saturday, but officials kept up their warnings.
Tropical-storm-force winds extend outward up to 240 miles (390 km) from its centre, according to the NHC.
Source: Fijian Broadcasting Cooperation