A flash flood warning was also issued in Riverside County for areas in Lake Elsinore, which were affected by the Holy Fire. Heavy rainfall expected in the area could cause flash floods, debris flows and rock slides.
Earlier Monday afternoon, the Riverside County Emergency Management Department issued a voluntary evacuation warning for those living in the following Cranston Fire burn areas: Hurkey Creek, Lake Hemet, Apple Canyon, Fleming Ranch.
The department posted to Twitter, urging residents in those areas to leave before the rain arrives.
Those in other areas impacted by past brush fires, such as the Holy Fire, were asked to monitor weather reports, place sandbags to protect their homes and prepare to leave at a moment's notice.
Dozers created a channel in the Lake Elsinore area to keep possible mudflows away from neighborhoods.
Rosa is also creating the potential for dangerous surf and rip currents off the coast.
South-facing beaches could see surf of up to 10 feet, along with strong rip currents on Monday.
Los Angeles County lifeguards are warning surfers about the currents. In Malibu, the currents are strong enough to push surfers into the pier and nearby rocks.
Rosa's force will last Monday through Wednesday.