(CNN) As Californians endure what could be the worst heat wave in state history, a rare hurricane offshore is poised to extend extreme temperatures already threatening rotating power outages and also deliver powerful winds that could fan raging wildfires.
Extreme heat, damaging winds and an increased fire threat will escalate across Southern California from Thursday through Saturday as Hurricane Kay -- forecast to make the closest pass to Southern California of any such storm since 1997 -- aims to approach the western coastline of Baja California.
Parts of Southern California will see dangerously hot conditions on Thursday and Friday, as Kay causes strong, hot and dry winds to blow toward the Pacific coast from inland desert regions -- similar to Santa Ana Winds, according to meteorologists. That hot air gets compressed as it moves through the mountains, causing temperatures to rise.
As a result, Los Angeles will push triple-digit heat Thursday and Friday, with temperatures between 100 and 112 -- with overnight temperatures set to fall only to the mid-70s to mid-80s. San Diego is under an excessive heat warning, with temperatures up to 97 degrees forecast.
Meantime, Kay's winds could gust over 60 mph as winds around the storm begin to interact with the mountainous terrain of Southern California. That could spell further trouble for firefighters battling the fast-moving Fairview Fire, which has burned more than 19,000 acres since it started Monday.
Kay should remain a hurricane until it gets to around 250 miles from San Diego -- something only four other storms have done since 1950, CNN meteorologists Derek Van Dam and Judson Jones said. It then "should reach a point about 130 miles southwest of San Diego Saturday morning as a weakening tropical storm," the National Weather Service in San Diego wrote Wednesday night, before petering out at sea.
The heat will then end "abruptly and unusually," the National Weather Service in Los Angeles said. That's when Kay's fringes are due to bring significant rainfall across Southern California and Arizona before pushing Saturday into Central California and Nevada, the Weather Prediction Center said.
Sweltering temperatures then are expected to give way to excessive rainfall, which can cause quick rises in creeks and rivers and could lead to flash flooding in Southern California and southwest Arizona.
"It's never a good thing to get too much rain all at once, a trait all too common among slow-moving tropical storms," the prediction center wrote Wednesday morning. "Thus, the flash flood potential is summarily also rapidly increasing."
Western states have sizzled for a week under triple-digital temperatures as an extended, record-breaking heat wave imposed brutal conditions across the region. Such extreme heat events are being pushed into unprecedented territory, scientists say, as planet-warming emissions worsen the human-caused climate crisis.
At least 10 places in California have set all-time high temperature records during the heat wave, while more set records for the monthly high temperature for September. On Tuesday, Sacramento hit 116 degrees, breaking the previous record of 114 set in 1925.
"This will be essentially the worst September heat wave on record, certainly in Northern California and arguably for the state overall," UCLA climate scientist Daniel Swain said Tuesday in a Twitter Spaces discussion. "By some metrics, it might be one of the worst heat waves on record, period, in any month, given its duration and its extreme magnitude."
"In some ways, this is the new normal," said Jan Null, a California meteorologist and owner of Golden Gate Weather Services.
The relentless heat wave has driven up demand for power and strained California's energy grid. Though rotating blackouts were avoided Tuesday, hundreds of thousands of Pacific Gas and Electric Company customers in California were warned to prepare for the possibility of controlled blackouts if energy falls short.
Residents for the ninth consecutive day Thursday were asked to set thermostats to 78 degrees or higher, avoid using major appliances and turn off all unnecessary lights between 3 p.m. and 10 p.m., per a Flex Alert issued by California Independent System Operator, which manages most of the state's power grid.
In neighboring Nevada, NV Energy is urging all customers to reduce electricity usage through Thursday, saying increased demand amid the heat wave could significantly reduce energy available for the state from Western energy markets.
This week's heat wave extends from British Columbia to northern Mexico under a huge area of high pressure that's effectively created a clear lid over the region. Within the so-called heat dome, high pressure acts as a lid on the atmosphere, causing hot air to sink and warm even more under the rays of a relentless sun.
The climate crisis is increasing how large heat domes can get, said Swain, the UCLA climate scientist. "Climate change has increased the frequency, the intensity, the duration, and also -- this is somewhat new evidence -- the spatial extent of heat waves," he said.
The extreme heat also means fires burn more intensely and for longer.
Numerous fires broke out over the past week and continue to blaze in Western states, including California, where a prolonged drought has created a hotbed of dry, dense vegetation ready to fuel infernos. At least four people have died in two California wildfires that also have displaced thousands, burned homes and scorched acres.
The Fairview Fire in Southern California swelled rapidly over parched vegetation and forced hundreds of residents to flee. Two people were killed as the flames spread. As of Wednesday night, the blaze had burned 19,377 acres and was 5% contained, officials said.
To the north, the Mountain Fire burning in Siskiyou County has scorched through 11,690 acres after igniting last week. Nearby, also in Siskiyou County, two women, ages 66 and 73, died in the Mill Fire, which has burned 3,935 acres and destroyed 118 structures as of Wednesday, according to Cal Fire.
The Mosquito Fire, burning in both El Dorado and Placer counties, began Tuesday and consumed 5,705 acres by Wednesday evening, forcing evacuations.
More than 245,000 acres collectively have burned in 6,100 wildfires in California so far this year, according to Cal Fire.