Strong winds in Santa Ana are creating dangerous fire conditions across Southern California during the first half of the week. The National Weather Service (NWS) office in Los Angeles has issued a rare Particularly Dangerous Situation Warning (PDS) due to the critical fire danger.

(MORE: What are Santa Ana winds?)

“Due to the expected long duration of dangerous fire weather conditions and critically dry fuels, there is an increasing risk that new ignitions will result in very rapid fire spread and extreme fire behavior,” the NWS Los Angeles office said in its forecast briefing.

P​DS red flag warnings are issued every three to five years in California.

At least one forest fire broke out overnight within these warning signals. The Franklin Fire in Malibu near Pepperdine University prompted some evacuations early Tuesday morning, according to the Associated Press.

Wind gusts of over 50 mph helped fan the fire, while relative humidity was in the single digits.

Areas with the highest risk: The strongest winds and highest risk will extend from the mountains northeast of the Santa Clarita Valley to the eastern valleys of Ventura County and south through the southern coastal portion of Ventura County. According to the NWS, the Calabasas, West Santa Monica and Malibu areas will also be heavily impacted by these winds.

Forecast time: Winds are expected to continue at peak intensity through Tuesday, particularly early. Wind gusts could reach speeds up to 60 to 80 miles per hour, causing trees and power lines to fall, causing outages and dangerous travel conditions.

Humidity levels in the single digits allow fires to be easily started and spread quickly.

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What causes this? A strong anticyclone forms in the Great Basin. This will bring an east-northeast wind across Southern California. As the winds are forced to force their way through the mountain passes and canyons, they accelerate, bringing with them dangerously strong winds.

When these winds are combined with dry conditions and low humidity, a high fire risk remains.

Most wind events in Santa Ana begin in the morning, but this time in the afternoon hours.

Meteorologists urged residents to remain vigilant. Make sure you have the ability to receive warnings and follow officials’ instructions about any fires. If evacuations are ordered, you must act quickly as any wildfires that develop spread quickly.

Jennifer Grey is a weather and climate writer for Weather.com. She has been reporting on some of the world’s biggest weather and climate stories for two decades.