Hot mountain winds will increase in the Santa Clarita and Grapevine areas Sunday, raising red flag warnings at 4 p.m., as a heat wave moves into Southrn California.

High pressure will strengthen over the area into early next week, National Weather Service forecasters said.

Except along the coast, triple digit temperatures will be likely Monday and Tuesday with very warm overnight low temperatures.

Gusty north winds will develop across the region, and will combine with hot temperatures, very low humidities, and very trees and brush.

That will bring “critical red flag conditions” to the Interstate 5 corridor through Tuesday. Any new fires will have the potential for very rapid fire spread and extreme fire behavior, the NWS said.

Particular concern was expressed for afternoon “sundowner” winds across the Santa Barbara county south coast and mountains.

Along the 5 Corridor, winds of 15 to 30 mph with gusts to 45 mph were possible Sunday evening through Monday night. And Sunday’s highs of up to 100 would increase to 103 Monday.

And the winds will be dry: humidity from 3 to 10 percent, even overnight, the NWS predicted.

While red flag warnings were not issued by the NWS for the Santa Monica Mountains, Hollywood Hills or the San Fernando and San Gabriel valleys, forecasters said fire risk would be elevated there.

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