A strong Pacific storm tapping into subtropical moisture is taking aim at California, raising the threat of flash flooding and debris flows.
Both mandatory and recommended evacuation orders have been issued for some areas, including parts of Santa Barbara and Ventura counties. See the full list here.
The National Weather Service says a strong storm system will be rolling ashore Tuesday, heading first to Santa Barbara County before bringing heavy rain to Los Angeles County on Wednesday.
Burn areas from recent wildfires in both counties may be susceptible to mud and debris flows.
Forecasters issued a flash flood watch for recent burn areas across southwestern California, while noting that the area of the watch may need to expand beyond those burn areas during the peak of the storm. The watch is set to expire Friday at 5 a.m.
Andrew Rorke, a senior forecaster with the NWS, says rain coming down in big bursts could spell trouble.
"If the 2-4 inches of rain falls gently over the whole 72 hour period, not a lot is going to happen," he said. "Unfortunately, we are forecasting a couple big bursts of rain."
NWS forecasters revised their predictions Monday afternoon, projecting the storm will drop 2 to 5 inches of rain for the coastal and valley regions and 5 to 10 inches in the foothills and mountains.
The so-called atmospheric river is expected to arrive Tuesday and last through Thursday night.
Rorke says they're keeping close watch on the Thomas Fire burn area.
"The intensity of this storm... is expected to be as intense, if not more intense, than what we saw back in January," Santa Barbara County Fire spokesperson Amber Anderson told KPCC.
Santa Barbara County Fire is working hard to prevent "anything as catastrophic" as the damage the area saw in January.
The greatest threat is bare hills following fires late last year, Anderson said, as they are more prone to mudslides.
"Our number one issue that we are preparing for is another debris flow, whether it's through Montecito or one of the other neighboring areas adjacent to some recent fire burn scars," Anderson said.
One problem for officials in January was how quickly the area became cut off, Anderson said, especially once the 101 and the 192 were closed due to debris flows. To combat that, they're placing equipment throughout the area.
"We don't know exactly where the storm is going to hit. That's always the number one unknown," Anderson said.
The number one thing the department is changing, according to Anderson: communication.
"Communication is always our number one challenge, but it is the number one way that we can improve, and that's what we're looking to do this time," she said. They want to improve communication both within their department and with the public.
Forecasters are also watching the La Tuna Fire burn area in Burbank.
The rain is expected to linger into Friday.
County emergency management director Rob Lewin says based on the forecast the storm will be the most powerful since the Jan. 9 deluge that triggered massive and deadly debris flows in Montecito.
Local officials are also working to move homeless people out of harm's way.
Teams from the L.A. County Sheriff's Department were out Monday in the San Gabriel River bed and will continue outreach to a growing homeless population along the river as the week progresses, said Sheriff's Commander Jim Hellmold.
"We want to ensure we get our homeless residents the resources they need, and more importantly, during this storm event, into safe conditions so that they're not swept away by stormwaters," he said.
The department stepped up routine outreach to homeless encampments in riverbeds after last year's particularly nasty fire season. Many flood-prone areas are also at heightened risk for fire after rains replenish vegetation.
In January, a task force convened in the wake of the Skirball Fire counted 191 homeless encampments on 76 fire-prone parcels of land within L.A. city limits.
LAPD officers are using that survey as well as their own information on encampments to target outreach in advance of the rains, said LAPD Commander Jorge Rodriguez.
Last week, with expected heavy rains, off-road motorcycle units visited the Sepulveda Basin and La Tuna Canyon Wash to hand out leaflets and provide information on shelters to homeless people camped deep in the brush. Rodriguez said some 100-150 people generally camp in the area.
He noted that in January, officers helped evacuate dozens after a storm caused flooding, "so we're hoping they can remember them needing to get evacuated and leave before the storm comes."
Pasadena police and fire officials are particularly concerned about flooding in the Arroyo Seco during upcoming rains, said city spokeswoman Lisa Derderian.
Outreach teams visited the area a few months ago and moved the area's homeless from the riverbed, she said.
"Most have stayed away," said Derderian.
Nonetheless, Pasadena police will visit the Arroyo during the rains to look for people who could get caught in any flooding, she said.
"We will keep an eye out," said Derderian. "Sometimes we get animals that fall into flooded conditions as well."
Pasadena Police will keep the department's helicopter in the air, weather permitting, to look out for anyone caught up by floods or other rain-related issues, she said.
MANDATORY EVACUATIONS
These evacuations go into effect starting Tuesday at 12 p.m.
SANTA BARBARA COUNTY
Mandatory evacuations have been issued for extreme and high risk areas, as seen on this map. This includes the Whittier and Sherpa fire burn areas, as well as part of the Thomas Fire burn area.
VENTURA COUNTY
Matilija Canyon
North Fork
Vista Fire Burn Area – Division Z
Vista Fire Burn Area – Division B
Nye Road; west: Highway 33; south: Nye/Highway 33
La Conchita
RECOMMENDED/VOLUNTARY EVACUATIONS
These evacuations also go into effect Tuesday at 12 p.m.
SANTA BARBARA COUNTY
Those in the Alamo Fire burn area are under recommended evacuation orders. See the affected area on this map.
VENTURA COUNTY
Casitas Pass Road, between Santa Ana Road & Rincon Road
Ojai Road, between Thomas Aquinas College Road and Reeves Road
Ojai Road, between Thomas Aquinas College and Bridge Road
East Ojai, from Gridley Road east to Reeves Road
Norway Tract, east side of Floral Drive
Ventura County
This story was reported with contributions from KPCC's Rina Palta, Mike Roe and Brianna Flores.
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