Watch: Road washes away as Tropical Storm Hilary hits California.

Tropical Storm Hilary drenched Southern California, dumping more than half an average year's worth of rain in one day.

Hilary, which was downgraded to a post-tropical cyclone overnight, left thousands of Southern California residents without power Sunday as storm conditions took down power lines.

Despite Hilary being downgraded to a post-tropical cyclone, it is still expected to bring heavy rain and significant flooding across the Southwestern United States as it heads northward, the National Hurricane Center said.

Hilary was the first tropical storm to cross into California from Mexico since Nora in 1997, the weather service office in San Diego said Sunday night. If Hilary had made landfall in California, it would have been the first tropical storm to do so since 1939.