Hurricane Hilary, a powerful Category 4 storm brewing off the coast Mexico's Baja California peninsula, is making its way towards the Pacific coast. It's projected to hit southwestern California as a tropical storm — the first since 1939 — by Monday, bringing dangerously high winds and torrential rain over the weekend.

The National Hurricane Center (NHC) forecasts Hilary will make landfall in Baja on Sunday as a hurricane but lose strength as it makes its way north. It's expected to hit Southern California as a tropical storm, peaking this weekend into Monday. Hilary's monsoonal rains will cause flash, urban and arroyo flooding on Saturday with the potential for "significant impacts," the NHC said.

The storm will envelop southwestern California, with San Diego, Orange, Riverside, San Bernardino and Los Angeles counties all under a flood watch from Saturday night through Monday night, according to National Weather Service predictions. The heavy rains could result in flooding of rivers, creeks, streams and low-lying areas.

"Although it is too soon to determine the location and magnitude of these impacts, interests in these areas should monitor the progress of Hilary and updates to the forecast," the NHC advised.

The last time the Golden State was hit by a tropical storm was on Sept. 24, 1939, when what was left of a hurricane became a deadly tropical storm which soaked Los Angeles with more than 5 inches of rain in 24 hours, the NWS said. Flooding from the storm killed 45 people and another 48 were killed out at sea. And at one point, the Eastern Coachella Valley was under 2 feet of water.

California's lack of preparedness for that storm led to the creation of a Southern California forecast office in February 1940.

The only known hurricane to hit the West Coast grazed San Diego on Oct. 2, 1858, with winds as high as 75 mph, just above the threshold for a hurricane.