The strongest storm of the season is heading for Southern California, expected to hit late Tuesday and dump heavy rain through Thursday. That means residents living near fire-scarred areas will again go into protective mode, trying to defend their homes from potential floods and mud flows before possibly evacuating their neighborhoods.

Updated National Weather Service tweet

Homes below the 426 square miles of terrain that burned in the Thomas Fire in Santa Barbara and Ventura counties as well as parts of Los Angeles County that also saw fires are the most vulnerable in the coming rain.

Urban flooding is also likely in areas that are slow to drain during rainstorms. That sometimes includes parts of Long Beach and a few other coastal zones.

Rain will begin to the north in San Luis Obisbo County Tuesday night, moving south through Santa Barbara and Ventura counties Wednesday. It will reach Los Angeles Wednesday night through Thursday morning, according to a forecast of the National Weather Service.

The storm is forecast to produce the highest rainfall totals so far this season. Showers could be heavy at times, capable of dropping one-half to three-quarters of an inch of rain within an hour. That’s enough to trigger flash flooding and debris flows.

Overall, the National Weather Service expects two to six inches of rain in coastal and valley communities, and between four to six inches on south and southwest facing foothills and mountains. Some south facing slopes could get up to 10 inches of rain.

The U.S. Geological Survey assesses the debris flow risk in areas below recent wildland fires. Burn areas most vulnerable from fires in 2017 include the La Tuna, Skirball, Creek and Rye fires in Los Angeles County, the Thomas Fire in Ventura and Santa Barbara counties and the Canyon 2 Fire in Orange County. Here's a list of risky burn areas, including those from previous years.

In Montecito, right as the rain first started around 3 p.m., there was a huge line of cars coming down the hill towards the 101 Freeway. The hillside neighborhoods were quiet. Most houses had empty driveways and locked gates. Nearly all had orange flyers taped to their mailboxes that said, “mandatory evacuation,” put there by Santa Barbara County Sheriff's deputies.

The evacuation notices on everyone’s mailboxes in the mandatory zones in Santa Barbara County, as seen on Tuesday, March 20, 2018. Taken on Toro Canyon Road in Montecito. Emily Guerin/KPCC

Almost the only people outside were a crew of arborists from Santa Barbara working in front of a house damaged in the January debris flow. José Guadalupe Hernandez was suspended by a rope, 30 feet up, using a chainsaw to trim an oak tree.

“We already have everything ready to go in the truck,” he hollered down. “If the water really starts coming, we’ll get down and we’ll get out of here!”

Tree trimmer tweet

There was still a huge amount of damage from the last major storm — houses ripped apart, piles of dirt and boulders in yards, roads that remain closed. Still, the creek beds looked clear of debris — so that's a good sign for the storm.

Hamid Khalessi was putting a few final sandbags in front of his garage on El Toro Road in Montecito before he got into his little blue Mercedes sedan and headed down towards Ventura to stay with family. The creek just downhill from his house overflowed during the previous storm in January, badly damaging some of his neighbors' houses.

“This time we’re not going to take any chances,” he said, "I heard it would be like 10 inches of rain total. The water gets really a lot of power, and acceleration. It’s more dangerous than the other time."

This is his fifth evacuation since the beginning of December, and he’s gotten good at it. It only took him two-and-a-half hours to get ready — down from a day the first time.

Jose Rocha and Oswaldo Arzate were filling sandbags with a shovel on Santa Elena Lane in Montecito, in front of a house heavily damaged in the January mudslide. It was starting to rain more heavily and no one else was around.

All the other houses were either damaged and unoccupied, or the owners had already evacuated. They were filling the bags with mud from the backyard of the house, and were glad to be working. Arzate said times were hard right now.

“If my boss allows me to work in the rain, I’ll work in the rain,” he said.

Santa Barbara County sent out an alert telling everyone in the mandatory evacuation area to get out — but they kept working.

Resources for storm info, sandbags, other emergency prep

Los Angeles County:

During heavy rains in December, mud flowed off burned hillsides and buried La Tuna Canyon Road, invading homes and garages in the area. Depending on the amount and intensity of rain, more mud could flow in that area.

Los Angeles County issued a forecast of possible mud and debris flows in the LaTuna Fire area from Burbank to Sun Valley, the Skirball Fire near Bel Air, the Creek Fire near Sylmar and the and Rye fire area near Valencia.

During a storm in January, an L.A. County Flood Control District debris basin in Burbank overflowed, sending waves of muddy water sweeping down a steep winding street. The overflow damaged about 25 homes. The damage was cosmetic and not structural and no homes were red-tagged as uninhabitable, Burbank emergency services coordinator Eric Baumgardner said Monday.

The basin is designed to overflow in a controlled release, so it is possible it could overflow again in a heavy rain storm, he said. However, the basin's capacity has been increased by about one-third since the January storm. So, the extra space could keep the basin from overflowing this week, he said.

Caltrans has cleared out the mud-clogged culvert where the 210 Freeway intersects La Tuna Canyon Road, spokesman Tim Weisberg said. Caltrans also did slope stabilization work to control erosion along freeways and state-maintained roads in other L.A. County burn areas.

Rain has brought some freeways to a halt in low-lying areas.

Caltrans has also taken measures to prevent flooding on several freeways that flooded last year, Weisberg said. In cases like in Sun Valley and downtown Los Angeles, where power outages caused freeway pumps to fail, Caltrans has positioned portable pumps closer to potential problem areas.

Los Angeles County has an online mudslide and flood hazard map that shows Long Beach is at risk of flooding.

Sign up for Los Angeles County emergency alerts: https://www.lacounty.gov/emergency/alert-la

Sign up for Los Angeles city emergency alerts: http://www.emergency.lacity.org/blog/emergency-alerts-sign-emergency-alerts-notifyla

Los Angeles County Public Works Department has a list of which county fire stations stock sand and sandbags. Los Angeles city also posts sandbag details. Residents of the county's 88 incorporated cities may check with their local fire stations.

Los Angeles County has an online storm resource guide. Fallen trees, blocked roads and other storm mishaps can be reported to Los Angeles County Public Works Dispatch at (800) 675-HELP (4357)

Orange County: The Canyon Fire 2 area, which is mostly in Anaheim and extends into county territory, is the most recent burn area where a flash flood or mud might affect homes. The Silverado Canyon area that had been of heightened concern in past years after a 2014 fire is not expected to have big mud flows this year, said Shannon Widor with Orange County Public Works.

Some low-lying parts of the county shoreline tend to flood in heavy rains, generally around Sunset Beach and Huntington Beach, so residents are advised to prepare with sandbags. The county is also setting up some short interlocking plastic walls, "kind of like Legos" to prevent water getting onto one flood-prone street in the north Tustin area, Widor said.

Sign up for emergency alerts: www.ocsd.org/divisions/fieldops/emb/alerts

Emergency updates at @OrangeCountyEOC

Orange County posts a list of where to find sandbags.

Ventura County: December's Thomas Fire started near Santa Paula and it burned for a month until a big January rain storm extinguished it. Those January rains were concentrated in a strong storm cell over Montecito in neighboring Santa Barbara County, which sustained terrible mudslides. That stalled storm cell spared Ventura County serious damage.

This coming storm could take a destructive path into Ventura County. Matilija Canyon, Ojai, and Ventura city neighborhoods bordering or below the Thomas Fire Area could be most vulnerable. Public Works Director Jeff Pratt said he's got "eyes all over the county" watching for mudslides and flooding in areas near the Thomas Fire burn area. But he wants residents to also use a new county website to track conditions themselves and decide when to evacuate.

"They don’t have to wait for evacuation notices from us," Pratt said.



The new site, www.vcemergency.com divides Ventura County's recent burn and hazard areas into ten different zones and displays rainfall totals in real time.



"They can see the weather coming, they know the threshholds that will trip the wire," Pratt said.



The county will issue voluntary evacuation orders if a half inch of rain falls within one hour. Those orders will become mandatory if rainfall hits three-quarters of an inch in on hour.

Sign up for emergency alerts: www.readyventuracounty.org/vc-alert

Sandbags are available at most Ventura County fire stations.

Santa Barbara County: Cleanup is still underway to remove the massive mudslide that tore through Montecito after heavy rains Jan. 9.

Santa Barbara County issued a pre-evacuation advisory Monday, telling residents living in the areas below the Thomas, Sherpa, Whittier and Alamo fires to be prepared to evacuate if heavy rains heighten the danger of mud flows. An interactive map of the most endangered areas is here.

Sign up for emergency alerts: https://readysbc.org/ or http://awareandprepare.org/

Santa Barbara County Office of Emergency Management also publishes a page of radio frequencies to monitor for emergency messages in English and Spanish if power or cell phone towers are out.

Sandbags are available from Santa Barbara County and the city of Santa Barbara.

Riverside and San Bernardino Counties:

The rain will hit the Inland Empire counties later Wednesday so much of the last-minute planning will be done on Tuesday, said Roni Edif, spokeswoman for San Bernardino County Public Works Department.

San Bernardino County emergency crews will be watching the Cajon area, Lytle Creek, Mount Baldy and Forest Falls communities for signs of flooding or mud flows, Edif said.

Riverside County hasn't had any of the larger fires in recent years, so the risk of mudslides and flooding is fairly low in the coming storm, said county spokesman Ray Smith. Flood control and transportation work crews will be monitoring potential trouble sites as they would normally do in a storm.

Sign up for Riverside County emergency alerts: https://rivcoemd.org/rivcoready/AlertRivCo

Sign up for San Bernardino County emergency alerts: http://wp.sbcounty.gov/cao/countywire/?p=1559

This story has been updated.