Hurricane Hilary reached Category 4 status on Friday morning, as the National Hurricane Center issued its first-ever tropical storm watch for Southern California.
The storm, off the west coast of Mexico, has maximum sustained winds of 145 miles per hour and watches have been issued for Baja California, and a tropical storm watch for San Diego and Orange counties.
Heavy rainfall is also expected in the inland mountains and desert regions, which are normally dry this time of year.
Hurricanes commonly form in August and September off the Mexican coast, bringing warm water and humid air to Southern California, but the storms themselves rarely move north. Most move west across the Pacific Ocean without hitting California. It is not clear where the hurricane will make landfall, but officials expect it to weaken by the time it nears the U.S. Rains are expected in interior regions by Saturday, and at the coast on Sunday, continuing into early next week as the storm moves north.