Rosa will begin weakening overnight into Saturday.
Swells generated by the hurricane were also expected to produce life-threatening surf and rip currents off Southern California.
The National Weather Service's San Diego office said Rosa could bring 5 to 8 feet of surf, with highs of 9 to 10 feet.
Some areas of Los Angeles County could see up to an inch of rain, according to the National Weather Service.
Rosa, with maximum sustained winds decreasing to nearly 120 miles per hour (195 kph), was now a Category 3 storm, coming down a notch on the five-step Saffir-Simpson Hurricane Wind Scale.
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The U.S. National Hurricane Center says Rosa should still be at tropical storm force when it hits the Baja California Peninsula and Sonora state Monday with flooding rains.
The latest forecast from the National Hurricane Center (NHC) shows the storm moving west at about 12 miles per hour on Thursday before slowing down and turning to the west-northwest on Friday.
Sergio had winds of 50 mph (85 kph) early Sunday and it was centered about 485 miles (780 kilometers) south of Manzanillo, Mexico. Rosa was expected to reach Baja California on Monday as a tropical storm.
Hurricane Rosa is a major hurricane in the Pacific that will impact Baja California next week with heavy rain and possible flooding for the Desert southwest.
Up to 4 inches could fall in Flagstaff, Payson and Prescott through Wednesday. Some areas could get up to 6 inches.