A storm system moving toward Southern California will bring a “long period” of steady rain across the region this week and could trigger debris flows in recent burn areas, forecasters said.

The storm is expected to drop 2 to 4 inches of rain along the coast and in the valleys in Los Angeles, Ventura and Santa Barbara counties, and 4 to 6 inches in the mountains between Tuesday afternoon and Thursday morning, said Todd Hall, a meteorologist with the National Weather Service in Oxnard. South-facing slopes could see up to 8 inches in some areas.

“It’s a type of system we’re not used to in Southern California,” Hall said, warning commuters about potential roadway flooding and traffic impacts in Malibu and Topanga Canyon. “I think some of our infrastructure will struggle to handle” it.

Rainfall rates could exceed a half-inch per hour, which is enough to cause mudflows and flash flooding.


“It could hit the Thomas burn area. We could see it in the La Tuna” burn area as well, Hall said.

A significant storm system still on track to bring rain to #SoCal Tue-Thu! Flash flooding possible in many areas, flooding& debris flows possible near recent burn areas. #CAstorm #Cawx pic.twitter.com/fNIvBrc489 — NWS Los Angeles (@NWSLosAngeles) March 18, 2018

Authorities in Santa Barbara County are on alert and warned residents below the Thomas, Sherpa, Whittier and Alamo fires to be ready to evacuate this week.


Rob Lewin, director of the Santa Barbara County Office of Emergency Management, said in a statement that this week’s deluge will be the “most powerful storm” since Jan. 9, when mudslides swept through Montecito, killing 21 people and destroying homes.

Parts of the Southland last week experienced rain-related complications. A mudslide closed Topanga Canyon Boulevard through the Santa Monica Mountains from Thursday through Saturday.

Topanga Cyn Blvd (SR-27) is OPEN between PCH & Grandview Dr.! One last boulder from earlier today and how the roadway looks now @LHSLASD @CHPWestValley pic.twitter.com/5C8RUy29I0 — Caltrans District 7 (@CaltransDist7) March 18, 2018

alene.tchekmedyian@latimes.com


Twitter: @AleneTchek