Volkswacht Bodensee - Firefighters brace for mudslides as storm moves into California

The remnants of a hurricane that hit Mexico could also bring strong winds that could further fan the Fairview fire, prompting wider evacuation orders.

The 24,000-acre (9,700-hectare) fire, which erupted on Monday at the midpoint of a ferocious heat wave, is continuing to spread, fanned by "extreme downslope winds" from nearby mountains, fire officials said.

"I have not seen a fire burn like this in Riverside County in my career," said Cal Fire division chief John Crater.

"It's a very stubborn fire. It's doing things that we just haven't seen."

An already widespread evacuation zone was expanded to cover more than 20,000 people as emergency managers tried to out-flank the fire and get ahead of the winds.

Sheriff's deputies were going door to door to urge residents to get out of harm's way.

At least two people have already died in the blaze, apparently trapped by fast-moving flames as they tried to flee.

Meanwhile, Hurricane Kay made landfall in Mexico on Thursday and began moving northwards.

Even as it weakened into a tropical storm, it was expected to bring heavy rain to parts of California and Arizona.

Forecasters at the National Weather Service said up to seven inches (18 centimeters) of rain could fall in the area around the fire, creating the risk of flash flooding and mudflows in areas where burned-out soil cannot absorb the sudden downpour.

"We could go from a fire suppression event into significant rain, water rescues, mudslides, debris (flows)," Jeff Veik of Cal Fire's Riverside Unit told a community meeting.

"We have challenging days ahead."

The tropical storm moving up from Mexico looked set gradually to bring an end to the punishing heat wave that has enveloped a large chunk of the western United States for more than a week.

But temperatures -- some of which have exceeded 110 Fahrenheit (43 Celsius) in places for multiple days -- remained high in central and northern California.

"Overnight lows will continue to rival records this weekend as the increased cloud cover traps warm air at the surface," the National Weather Service said.

"Approximately 29 million Americans are currently under an Excessive Heat Warning."

The warm and dry air was also increasing the chances of fires over a vast area, a risk that was being further elevated by winds that are whipped up as pressure systems move around.

The western United States is more than two decades into a historic drought that scientists say is being worsened by human-made climate change.

Much of the countryside is parched and overgrown, creating the conditions for hot, fast and destructive wildfires.

Climatologists predict that as the Earth continues to warm because of the unceasing burning of fossil fuels, these conditions will further worsen.

C.Kovalenko--BTB