Parts of Southern California were put under a tropical storm watch for the very first time Friday, as Hurricane Hilary grew to Category 4 strength and was poised to hit the region as a tropical storm

Considered "large and powerful" by the National Hurricane Center, Hilary was about 360 miles south-southwest of Cabo San Lucas, Mexico, 

A tropical storm watch was put in place Friday from the California-Mexico border to the Orange-Los Angeles county line, and included Catalina Island, meaning tropical storm conditions are expected generally within the next 48 hours.

The storm is forecast to weaken as it approaches Southern California, but parts of the state could see impacts as soon as Saturday

San Diego could see rainfall by Saturday evening, while Los Angeles residents could expect rainfall Sunday afternoon

Hilary is expected to weaken into a Category 3 hurricane by late afternoon Saturday, and diminish into a tropical storm by Sunday afternoon.

Emergency response workers across Southern California were handing out sandbags in preparation for the potential of severe flooding

Forecasters said Hilary could bring more than a year's worth of rain to the Palm Springs area, about 5 inches.

Hilary could be the first tropical storm to make landfall in California since 1939, according to federal weather officials.

How much rainfall could Hurricane Hilary bring?

– Coast/Valleys: 2-2.5 – Mojave Desert: 3-5 – Mountains: 4-10, with up to 12 inches on the eastern mountain slope – Lower Deserts: 4-7

Hurricanes need two things to stay energized: warm water and favorable winds. The California coast typically benefits from cooler water that flows southward along the coast and winds tend to either shear the tops off hurricanes or push them westward out to sea

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