From inland Southern California to much of the Bay Area, people across the state are facing dangerous heat Thursday as a fall heat wave nears its end, with daily temperature records in striking distance and forecasts in some areas showing highs near or above 100 degrees.

In the Los Angeles County valleys, the “unseasonably warm” temperatures will peak in the 90s and 100s, up to 20 degrees above average for this time of year, according to Ryan Kittell, a meteorologist with the National Weather Service office in Oxnard.

“The high temperatures are high enough to ... warrant concern,” Kittell said. “Sensitive populations, vulnerable populations are at an elevated risk for heat illness,” which includes the very young and old, those without air conditioning, pregnant people or those working outdoors for much of the day.

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Heat advisories are in effect Thursday from 10 a.m. to 8 p.m. for the Los Angeles, San Diego and Ventura County valleys, inland Orange County and the Santa Monica and Santa Susana mountains and the Palos Verdes Hills. Temperatures between 94 and 101 degrees are expected in the valleys and Santa Monica Mountains, and highs between 85 and 93 degrees are forecast in the Palos Verdes Hills.

Preliminary readings showed a few areas either matched or surpassed their previous daily record-high temperatures, according to the National Weather Service. Woodland Hills reached 102 degrees, beating the previous record of 101 set in 1991. Sandberg, a small community in the Antelope Valley, reached 86 degrees, surpassing the previous record of 84 in 2003. Up in San Luis Obispo County, Paso Robles matched the daily record of 99 degrees, first set in 1984.

A deep marine layer along the coast will keep the worst of the heat to inland areas.

However, almost the entire Bay Area — from the coastline to the mountains — is under a heat advisory through 11 p.m. Thursday, with temperatures nearing 100 degrees from the southern Salinas Valley to the San Francisco peninsula.

Kittell said the warming over the state is primarily caused by a ridge of high pressure over much of the southwest, as well a light offshore flow coming from the east.

“Those two factors tend to warm up the area,” he said.

Temperatures in the Central Valley will also be unseasonably high, reaching the mid-90s in much of the San Joaquin Valley, though no advisories have been issued.

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Officials also warned of dangerous surf and swimming conditions in the Bay Area and in parts of Southern California; Kittell urged anyone going in the water to stay near lifeguard stands.

By Saturday, temperatures will drop substantially across the state — in Southern California, by as much as 10 degrees, Kittell said.

“Tomorrow [Friday] should be a few degrees cooler and then significantly cooler on Saturday,” Kittell said. “And even cooler still on Sunday, when we’ll get generally highs in the 70s.”

A low-pressure system is forecast to move into Northern California this weekend, moving south by Monday, which could even bring a chance for rainfall early next week.