A red flag warning signifying a high risk of wildfire will be in effect Monday in the San Gabriel Mountains, the Angeles National Forest, the Santa Clarita Valley and several areas of neighboring Ventura County because of strong winds, high heat and low humidity at the start of the Southland’s first heat wave of Fall 2020.

“Critical fire weather conditions are anticipated across the mountains of Ventura and Los Angeles counties as well as the Santa Clarita Valley Monday morning through Monday afternoon,” warned a National Weather Service statement. “North to northeast wind gusts between 30 and 45 mph are expected along with relative humidity dropping into the teens and single digits. Therefore, red flag warnings have been issued for these areas from 5 a.m. Monday through 5 p.m.”

The weather Service said offshore winds combined with hot and dry conditions will bring elevated to brief critical fire weather conditions Tuesday through Friday in areas away from the coast, including an increased threat of plume-dominated fires with extreme fire behavior at times.

In the Santa Clarita Valley and the San Gabriel Mountains, a wind advisory will be in effect from 3 a.m. to 3 p.m. because of expected northeast winds of 20 to 25 miles per hour and gusts of 40 mph amid triple-digit temperatures.

“Gusty winds will blow around unsecured objects and make driving difficult, especially for high-profile vehicles’ warned the NWS. “Tree limbs could be blown down and a few power outages may result. Hot temperatures may cause heat illnesses to occur.”

Additionally, a heat advisory issued because of high temperatures will be in force from 10 a.m. Tuesday to 8 p.m. Thursday in the Santa Clarita, San Fernando and San Gabriel valleys, the Santa Monica Mountains, metropolitan Los Angeles, beach cities, the Hollywood Hills and inland Orange County.

“Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors,” warned an NWS statement, adding that children, seniors and pets must never be left unattended in vehicles, whose interior temperatures can quickly become lethal.

Partly cloudy skies were forecast in L.A. County Monday closer to the coast along with sunny skies in interior locations and highs of 77 degrees in Avalon; 79 at LAX; 84 on Mount Wilson; 86 in Long Beach; 87 in Downtown L.A.; 94 in San Gabriel, Palmdale and Lancaster; 95 in Pasadena; 96 in Burbank; 97 in Saugus; and 100 in woodland Hills. High temperatures will linger at least through Sunday.

Sunny skies were forecast in Orange County Monday, along with highs of 74 degrees in San Clemente; 75 in Newport Beach and Laguna Beach; 80 on Santiago Peak; 87 in Irvine; 88 in Fullerton; 89 on Ortega Highway at 2,600 feet and in Mission Viejo; 91 in Anaheim; 92 in Yorba Linda; and 93 at Fremont Canyon and Trabuco Canyon. Similar temperatures are expected through Sunday. No special advisories were in effect in Orange County as of Monday morning.

Los Angeles reopened a number of cooling centers Sunday, Mayor Eric Garcetti announced. The following centers are open from noon to 6 p.m.:

— Platt Branch Library, 23600 Victory Blvd., Woodland Hills, 818-340-9386

— Mid-Valley Regional Library, 16244 Nordhoff St., North Hills, 818-895-3650

— Sun Valley Branch Library, 7935 Vineland Ave., Sun Valley, 818-764-1338

— Lake View Terrace Branch Library, 12002 Osborne St., Lake View Terrace, 818-890-7404

— Eagle Rock Branch Library, 5027 Casper Ave., Los Angeles, 323-258-8078

— Vernon Branch Library, 4504 S. Central Ave., Los Angeles, 323-234-9106

— Buena Vista Branch Library Meeting Room, 300 N. Buena Vista St., Burbank, 818-238-5202

Social distancing requirements due to the coronavirus pandemic have resulted in reduced capacity at the sites.

>> Want to read more stories like this? Get our Free Daily Newsletters Here!