Southern California is under a tropical storm watch for the first time on record, according to the National Weather Service.

Parts of the Golden State could see unprecedented rain over the weekend from Category 4 Hurricane Hilary, which on Friday was working its way northward south of the coast of Mexico’s Baja Peninsula.

Hilary was a Category 4 monster with sustained winds of 145 mph as of Friday afternoon, but the National Hurricane Center expects the storm to weaken as it moves into cooler waters off the northern coast of Mexico and southern California.

Here’s the track map for Hilary:

But Hilary is poised to bring a deluge of rain along with it — and some areas could get more rain over the weekend than they get in several years.

The National Weather Service office in San Diego was warning Californians about what could be a catastrophic rainfall event:

As of 1 p.m. CDT Friday, the center of Hurricane Hilary was located about 360 miles south-southwest of Cabo San Lucas, Mexico, and was moving northwest at 10 mph.

Hilary had 145 mph winds, making it a solid Category 4 hurricane.

The hurricane center said that Hilary should begin to weaken by Saturday. It will likely still be a hurricane when it reaches the Baja Peninsula but should be a tropical storm by the time it reaches southern California.

Hurricane and tropical storm warnings stretched along the Baja Peninsula in Mexico on Friday (from Punta Abreojos to Punta Eugenia), but it’s the tropical storm watch for southern California that was making the headlines.

The hurricane center said the first-ever tropical storm watch for California stretched from the Mexico border northward to the Orange/Los Angeles county line and also included Catalina Island.

The hurricane center said that on the forecast track the center of Hilary will move close to the west coast of the Baja California peninsula over the weekend and reach southern California by Sunday night.

Hilary’s worst and heaviest rain will likely be on the north and east side of the center, which puts parts of California in line to recieve potentially a year’s worth of rain in just a few days.

The hurricane center said heavy rain will be possible in the Southwest U.S. through next Wednesday, peaking on Sunday and Monday. Three to 6 inches of rain, with isolated amounts of 10 inches, are expected across portions of southern California and southern Nevada.

“Rare and dangerous flooding will be possible,” forecasters said.

The hurricane center was also tracking four tropical waves in the Atlantic that have the potential to become storms next week. One area of interest next week will be in the Gulf of Mexico but as of Friday afternoon has a low chance of development.