A flash flood watch issued for Riverside County and parts of Orange County, including areas affected by the Holy Fire, remained in effect through early Friday morning as a powerful fall storm pummeled Southern California Thursday.
The watch was extended through 3 a.m. Friday in Orange County inland areas, Riverside County mountains, San Bernardino County mountains, as well as the Santa Ana mountains and foothills.
Flash flooding is "likely" and possible debris flows are possible in the Trabuco Canyon area of Orange County, where the Holy Fire raged in August, according to the National Weather Service reported earlier in the day.
Both are also a concern in other canyons in the area, including Indian, Horsethief, Temescal and Coldwater canyons, according to he agency.
More than a thousand homes and 3,500 people were under mandatory evacuation orders in Riverside County ahead of the storm, but many have not left, Cal Fire Riverside Capt. Fernando Herrera told KTLA.
He said those residents could pose a problem for first responders and rescuers if significant rains case flooding or debris flow.
“Now we have to take care of welfare of those people,” Herrera said, adding that they would need to evacuate or shelter in place if an emergency occurs.
Residents in the communities of Amorose, Alberhill, Glen Ivy A, Glen Eden, Grace, Horsethief A, Laguna A, Matri, McVicker A, Rice, Withrow A remain under mandatory evacuation.
Residents in Trabuco Creek in Orange County are under mandatory evacuation, while those who live in Rose Canyon are under a voluntary evacuation warning, the Orange County Sheriff's Department said Thursday. The Mystic Oaks and El Cariso areas were under voluntary evacuation warning on Wednesday.
In addition, a "soft road closure" has been issued at Trabuco Canyon and Rose Canyon roads for possible flooding and debris flow in Orange County. The area will be closed to recreational traffic, but residents will have access, according to the Orange County Sheriff's Department.
Knotts Berry Farm in Buena Park closed Thursday because of "inclement weather," according to a tweet from the theme park.
Riverside County officials warned residents of possible evacuations as early as Monday, when warnings were issued.
Barriers and sand bags were left in areas where debris flows were a concern. There is also a large Riverside County Sheriff’s Department presence in those areas to help residents.
Communities in Riverside and Orange counties could expect around half an inch to 1.5 inch of rain Wednesday night to Friday morning, according to the National Weather Service. Some areas in the mountains could see more than 4 inches of precipitation.
The heaviest rainfall is expected to be the most intense between 7 a.m. and noon, Herrera said.
“This entire area is just a huge scar,” he said. “There is no vegetation, there is nothing left to hold the rain down. The soil itself is damaged. We have a lot of ash that makes it really silky and the water can’t penetrate into the soil, so you’ll get all that runoff immediately.”
A flood advisory is also in effect in San Bernardino County, and another one is also in effect through 9:15 a.m. for the areas affected by the Woolsey Fire in Ventura and Los Angeles counties.
The Holy Fire burned in the Trabuco Canyon area in August and scorched nearly 23,000 acres along the Riverside and Orange County line.