Hurricane Hilary churned off Mexico’s Pacific coast Friday as a powerful Category 4 storm threatening to unleash torrential rains on the mudslide-prone border city of Tijuana before heading into Southern California as the first tropical storm there in 84 years.

While it heads north, Hurricane Hilary is also threatening to bring record rainfall to western Pima County Saturday, Aug. 18 and Sunday Aug. 19.

The county’s Public Works and Communications departments are offering resources for anyone who may need help.

MyAlerts Flood Alerts Messaging:

People may sign up for notifications through the MyAlerts registrar.

Precipitation & Streamflow Data:

Real-time rainfall, storm water runoff and other weather conditions impacting neighborhoods are vieweable at the county’s Precipitation and Streamflow Data page.

Flood Prone Areas:

Expected rains also increase the chances of danger in areas prone to flooding. The county maintains a list of areas viewable on the Road Closures Update page.

Sandbag availability:

Arivaca fire station at 16091 W. Universal Ranch Rd. East Snyder Road and North Lason Lane Mt. Lemmon at East Carter Canyon Road and North Sabino Canyon Parkway Catalina fire station at 3885 E. Golder Ranch Dr. North Pima Canyon Drive and East Ina Road East Dawson Road and South County Club Road Pima County Mission Yard at 1313 S. Mission Rd. Fire station at South Camino Verde and West Ajo Highway Fire station at Trico Road and Silverbell Road Fire station at 6625 N. Sandario Rd. North La Canada Drive and Paseo Del Chino in Green Valley Vail fire station at 14550 E. Sands Ranch Rd.

Forecasters warned the storm could cause extreme flooding, mudslides and even tornadoes across the region.

Hillary grew rapidly in strength early Friday before losing some steam in the afternoon, with sustained winds falling from 145 mph to 130 mph (215 kph). Nevertheless, it was forecast to still be a hurricane when approaching Mexicos Baja California peninsula on Saturday night and a tropical storm when approaching Southern California on Sunday.

No tropical storm has made landfall in Southern California since Sept. 25, 1939, according to the National Weather Service. The watch was posted for a wide swath of Southern California from the coast to interior mountains and deserts. The U.S. National Hurricane Center warned of potential threats to life and property.

The latest forecast pointed to Hilary making landfall along a sparsely populated area of the Baja peninsula Sunday, about 200 miles south of the Pacific port city of Ensenada.

As it moves north, it could bring heavy rains to Tijuana. Mayor Montserrat Caballero Ramirez said the city was tracking the storm closely and clearing out storm drains.

The sprawling border metropolis of 1.9 million people is particularly at risk of landslides and flooding, in part because of its hilly terrain. Shacks are perched on cliffs with little vegetation to hold soil in place. In addition, dozens of people live under tarps on the streets and in canals in flood zones, including migrants who arrive daily from various parts of the world.

The city was setting up four shelters in high-risk zones and warning residents in risky zones, Caballero Ramirez said.

We are a vulnerable city being on one of the most visited borders in the world and because of our landscape,” she said.

Mexico issued a tropical storm watch for parts of mainland Mexico and put 18,000 soldiers on alert.

At midafternoon Friday, Hilary was centered about 325 miles south-southwest of Cabo San Lucas, near the southern tip of the Baja peninsula. It was moving northwest at 12 mph and was expected to turn more toward the north.

Some Cabo San Lucas schools were being prepared as temporary shelters, said Flora Aguilar, a city official.

In La Paz, the picturesque capital of Baja California Sur state on the Sea of Cortez, police patrolled closed beaches to keep swimmers out of the whipped-up surf. Schools were shut down in five municipalities.

It was increasingly likely that Hilary would reach California early Monday while still at tropical storm strength, though widespread rain was expected to begin as early as Saturday, the National Weather Services San Diego office said.

Hurricane officials said the storm could bring heavy rainfall to the southwestern United States, dumping 3 to 6 inches in places, with isolated amounts of up to 10 inches, in portions of southern California and southern Nevada.

Two to three inches of rainfall in Southern California is unheard of for this time of year, said Kristen Corbosiero, a University of Albany atmospheric scientist who specializes in Pacific hurricanes. Thats a thats a whole summer and fall amount of rain coming in probably 6 to 12 hours.

The region could face once-in-a-century rains and there is a good chance Nevada will break its all-time rainfall record, said meteorologist Jeff Masters of Yale Climate Connections and a former government in-flight hurricane meteorologist.

President Joe Biden said the Federal Emergency Management Agency had pre-positioned staff and supplies in the region.

I urge everyone, everyone in the path of this storm, to take precautions and listen to the guidance of state and local officials, Biden told reporters Friday at Camp David, where he is meeting with the leaders of Japan and South Korea.

Cities across the region, including in Arizona, were offering sandbags to safeguard properties against floodwaters, while the National Park Service planned to close vulnerable areas of Joshua Tree National Park, east of Los Angeles, on Friday evening, and suspend all back country camping.

Deputies with the Los Angeles Sheriff’s Department were driving on service roads to announce warnings over public address systems and urge homeless people living in riverbeds to move into shelters before the storm hits.

Janice Hahn, chair of the Los Angeles County Board of Supervisors, said planning had been underway for several days, which included evacuation plans for the tourist destination of Santa Catalina Island, off the coast.

I dont think any of us I know me particularly never thought Id be standing here talking about a hurricane or a tropical storm, Hahn said.

Officials in Southern California were also re-enforcing sand berms, built to protect low-lying coastal communities against winter surf, like in Huntington Beach, which dubs itself as Surf City USA.”

In nearby Newport Beach, Tanner Atkinson waited in a line of vehicles for free sandbags at a city distribution point.

I mean a lot of people here are excited because the waves are gonna get pretty heavy,” Atkinson said. “But I mean, its gonna be some rain, so usually theres some flooding and the landslides and things like that.

SpaceX delayed the launch of a satellite-carrying rocket from a base on Californias central coast until at least Monday. The company said conditions in the Pacific could make it difficult for a ship to recover the rocket booster.

Storms dont usually hit Southern California because prevailing winds usually push them either due west into open ocean or northeastward into Mexico and other parts of the U.S. Southwest, according to experts.

Almost all of them just go out to sea. Thats why we never hear about them, said Kerry Emanuel, a hurricane professor at Massachusetts Institute of Technology.

That’s unlikely to happen with Hilary mostly because of a high pressure heat dome that is expected to bring triple digit heat indices in the Midwest and block the eastern turn, Masters said.