Tropical Storm Hilary struck Mexico’s Baja California coast Sunday as concerns mounted over the storm causing what could be deadly flash flooding in the border city of Tijuana, Southern California and places as far north as Idaho that rarely get such heavy rain.

Hilary made landfall in a sparsely populated area south of Ensenada.

The storm has already caused flooding in places across Mexico’s arid peninsula and threatens to unleash torrential rains on mudslide-prone Tijuana, where many houses cling to steep hillsides, as it moves northward as the first tropical storm to hit Southern California in 84 years.

Forecasters warned the storm could cause extreme flooding, mudslides and even tornadoes. No tropical storm has made landfall in Southern California since Sept. 25, 1939.

Parts of the U.S. Southwest could be hit with once-in-a-century rains and there is a good chance Hilary could break all-time records as the wettest known tropical cyclone to douse Nevada, Oregon and Idaho.

This is a breaking news story. It will be updated.