The US National Hurricane Centre has warned of catastrophic and life-threatening flooding as Tropical Storm Hilary moves into southern California after making landfall in Mexico. 

Tropical storms rarely hit California, with US media reporting that Hilary would be the first such event for 84 years. Schools were ordered to close on Monday as the system approached and a state of emergency was declared for much of the state’s south. 

“Across the southwestern US, the ongoing and potentially historic amount of rainfall is expected to cause life-threatening to locally catastrophic flash, urban and arroyo flooding including landslides, mudslides and debris flows through early Monday morning,” the centre says 

Rainfall amounts of 3-6 inches, with isolated maximums of 10 inches, are expected across portions of southern California and southern Nevada, while totals of 1-3 inches are expected across areas of Oregon and Idaho, with local maximums of up to 5 inches through Tuesday morning. 

Residents were also warned of the threat from strong winds, thunderstorms and increased ocean swells as the storm system moves north.  

“Winds could be particularly strong and gusty in and near areas of elevated terrain,” the National Hurricane Centre says. “Higher gusts are expected well inland and will persist even after the system becomes post-tropical.” 

Southern California was severely hit by a tropical storm in September 1939, with 45 people killed in floods and extensive damaged caused to structures along the coast. Residents were described as generally unprepared as the event highlighted the risks. 

That Atlantic and Pacific hurricane season lasts until November 30.