The threat of wildfire will hang over the Southland beginning Friday night due to dry vegetation, low humidity and strong Santa Ana winds, the National Weather Service said.

A red flag warning will be in effect Friday evening through Sunday evening in most of Los Angeles and Ventura counties, including the LA basin.

Northeast winds between 15 to 25 mph will hit Friday night. By Saturday morning, winds will increase between 20 to 30 mph across mountain and forest areas, with gusts to 45 mph. Humidity levels will drop throughout the weekend, reaching between 8 and 12 percent by Sunday, the NWS said.

"Relative humidity is coming down into the single digits and teens, so if a fire is ignited, that can cause extreme fire behavior," said meteorologist Crystal Egger.

"Keep in mind, the severe drought has weakened many trees across Southern California. Wind gusts less than 50 mph can topple trees," Egger said.

The critical fire conditions will not apply to the San Gabriel and Antelope valleys but will be in effect in the coast and valleys of Ventura and Los Angeles counties, as well as Malibu to the Hollywood Hills of the Los Angeles Coast.

"Increasing offshore flow is expected Friday evening into early Saturday morning as high pressure builds into the Great Basin,'' the NWS said. "The strongest winds are expected late Friday night through Saturday afternoon, but moderate northeast winds will likely persist through much of the day Sunday.''

During this Santa Ana wind event, the California Department of Forestry and Fire Protection will bring in an additional 15 engines from Northern California to support local resources in Ventura, Los Angeles and San Bernardino counties, Cal Fire Capt. Mike Mohler said.

Winds will begin to subside Sunday evening, and humidity levels will rise early next week. Temperatures, meanwhile, will be around 10 degrees above normal, with highs reaching the low to mid 80s through the weekend.

Expect to see temperatures drop 20 to 25 degrees by Thanksgiving Day, Egger said.

City News Service contributed to this report.