Scorching temperatures continued to bake Southern California on Sunday, with a record of 121 degrees set in Los Angeles County and at least one death, a 41-year-old hiker, suspected to be related to the heat.
The record 121-degree reading, in Woodland Hills in the San Fernando Valley, northwest of downtown Los Angeles, eclipsed a record of 119, set in July 2006, according to Dave Bruno, a meteorologist with the National Weather Service’s Los Angeles/Oxnard forecasting office.
“When all is said and done, there will probably be a dozen official records today, at least daily records, and several monthly or all-time records today,” Mr. Bruno said.
“Very, very hot day,” he added. “Some places never fell below 100 degrees last night, which is very unusual around here. This is quite a heat wave.”
The region was locked in a heat wave because of a high-pressure system and an offshore flow that prevented the sea breeze from cooling the shore. This gave rise to conditions that “allowed basically the entire region to roast,” Mr. Bruno said.
An excessive heat warning was issued by the National Weather Service on Sunday night for parts of Southwest California, including parts of Los Angeles, Ventura, Santa Barbara and San Luis Obispo Counties. It will remain in effect until Monday night at 8 p.m.
Monday is expected to be slightly cooler, but on Tuesday night and Wednesday, meteorologists expect Santa Ana winds, which could worsen fires around the state, Mr. Bruno warned. High temperatures and low humidity dry out vegetation, and aided by the winds, a tossed cigarette, an improperly extinguished campfire or a spark from a car could ignite a blaze.
On Sunday, Burbank tied its highest temperature of 114 degrees; downtown Los Angeles reached 111 degrees, just shy of the record of 113 set in December 2010, but surpassing the previously held Sept. 6 record high of 102. Some places in the foothills did not drop below 100 degrees overnight, Mr. Bruno said.
All sites monitored by the forecast office in Sacramento set or tied records, including Red Bluff, where a temperature of 113 degrees broke the previously held record of 109 set in 1957.
The Los Angeles Sheriff’s Department search and rescue team was called to the aid of a 41-year-old hiker around 1:30 p.m. on Saturday, said David Katz, team leader of the group. The woman, who had begun hiking Tapia Park in Malibu Creek State Park around 8 a.m. that morning, had a seizure and paramedics were unable to resuscitate her. A report from the medical examiner on the cause of death was pending.
There were three other heat-related rescues on Saturday, Mr. Katz said. The hiker’s death prompted state and national parks in the area to close for the weekend, but despite official recommendations to not hike, Mr. Katz saw lots of people on Sunday morning.
“In my 30 years in Malibu I’ve never seen this,” he said, adding that in Malibu, ocean breezes usually keep temperatures relatively cool. “There is no respite right now.”
On Labor Day weekend last year, the group carried out nine heat-related rescues, he said, including one fatality. The group also rescues lots of overheated dogs each year.
The California Independent System Operator, or ISO, which oversees the state’s electrical grid, declared a Stage 2 emergency on Saturday when attempts to extinguish wildfires took out 1,600 megawatts of resources in Southern California.
The heat wave has placed a demand on energy that goes beyond the current supply, the organization said in a statement. Earlier, it had issued a statewide alert that called for residents to conserve energy from 3 p.m. to 9 p.m.
“The ISO recognizes that reducing energy use during the hot time of the day is a hardship, especially for those working from home or for families with children schooling at home,” it said in a statement on Saturday. “However, if a large enough number of consumers conserve even in small ways, they can help grid operators avoid more serious system emergencies.”
The heat wave had a widespread impact across Southwestern states, according to the National Weather Service. Las Vegas set a high of 114 on Sunday, dethroning the previous record of 110 from 1955, and Phoenix recorded a high of 113 degrees, breaking the previously set record of 111 from 2013. In Colorado, temperatures in the Denver area reached the high 90s over the weekend, breaking records for early September.