Surface high pressure that has built into the Great Basin is helping to strengthen the offshore flow over L.A. and Ventura counties, generating a moderate Santa Ana wind event over the San Gabriel Mountains in both counties, producing winds of 35 to 45 miles per hour, said the National Weather Service.
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"This combined with humidities lowering into the single digits will create several hours of critical fire weather conditions to this area,'' according to an NWS statement.
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The red flag warning will be in effect from 3 a.m. to 6 p.m. Friday in the San Gabriel Mountains in L.A. and Ventura counties, the Angeles National Forest, Ventura County's Los Padres National Forest, the Santa Clarita Valley, Orange County's Santa Ana Mountains and inland Orange County cities.
The warning comes as firefighters continue to battle a brush fire near Redlands that has charred over 125 acres. The blaze, which erupted Wednesday night, was 50% contained as of Friday morning.
So far this year, wildfires have burned 1.4 million acres across California amid hot, dry and windy conditions.
RELATED: California sets record after millions of acres burned so far this year
Northeast winds of 20 to 30 miles per hour with gusts of up to 45 mph will blow in the San Gabriels in and around the 14 Freeway corridor amid humidity levels as low as 6 percent. The warning replaces the somewhat less serious fire weather watch that was in effect Thursday.
With the red flag warning, L.A. County Fire has pre-deployed resources.
"Not only do we have strike teams prepositioned in known fire corridor areas to increase that response level, we've also staffed water tenders as well, " said L.A. County Fire Inspector Sean Ferguson
Meanwhile, a heat advisory will be in effect until 5 p.m. Friday along the Los Angeles County coast, in Malibu, Santa Monica and other beach cities, in downtown Los Angeles, Hollywood, Beverly Hills, the San Gabriel and Santa Monica mountains, the San Fernando, Santa Clarita and San Gabriel valleys, and inland Orange County, indicating temperatures could threaten human health.
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"Hot temperatures may cause heat illnesses to occur,'' warned a weather service statement. "Those without air conditioning will be especially vulnerable during this extended heat wave. Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors.''
The NWS said a record high for an October 15 was set Thursday in Woodland Hills, where the high was 105, and the record high 86 in Sandberg tied the record set in 1991.
City News Service contributed to this report.