By Gary Robbins, Rob Nikolewski, The San Diego Union-Tribune The Tribune Content Agency
The worst Santa Ana windstorm in years is expected to arrive in San Diego late Monday and lash the region into Wednesday, potentially sparking wildfires, snapping trees and ripping apart outdoor Christmas lights from the mountains to the sea, the National Weather Service and San Diego Gas & Electric say.
In a rarity, the utility has notified more than 117,000 customers that it might temporarily shut off their power to reduce the threat of wildfires, and that outages could last a day or more.
"The winter rains just haven't shown up, and it's creating some very critical fire weather conditions this year," said Brian D'Agostino, SDG&E's vice president of wildfire and climate science.
The potential for damage also will be high because the winds will be unusually powerful, and the relative humidity will be very low. Winds could gust upwards of 70 mph in the mountains, 50 mph to 60 mph along parts of Interstates 8 and 15, up to 40 mph on state Route 76 and 30 mph at the coast.
Forecasters say the winds will be well-established in East County by midnight and will begin whipping snapping some coastal areas by sunrise Tuesday.
Some of the strongest gusts are likely to follow a corridor from the Ramona and Escondido areas all the way to Encinitas and Del Mar. Winds also will sweep across Camp Pendleton and along a stretch of Interstate 8 east of Alpine that's well-known for wind-related traffic accidents.
The potential for widespread fires hasn't been this high since the first week of December 2020, when fire broke out across many areas of the county.
"The highest-risk areas for this particular event ... are going to develop (in) areas above 3,000 feet," D'Agostino told reporters Monday morning, adding that gusts are expected to blow through wide stretches of rural and backcountry areas carpeted with chaparral, one of the country's most flammable kinds of vegetation.
"As we head up Boulder Creek Road towards the western slopes of Cuyamaca, we think winds there could easily hit hurricane force through this event," D'Agostino said.
SDG&E expects to institute public safety power shutoffs - pre-emptively de-energizing power lines to reduce the risk that high winds could knock them down into dry vegetation and spark a wildfire.
Last month, Santa Ana winds that reached 50 mph led to 1,263 SDG&E customers losing power - but this incoming wind storm will be much stronger. The utility has already warned about five times the number of customers of potential outages from this series of Santa Anas.
"This is actually the highest fire potential we have seen in San Diego County in six years," D'Agostino said. "We have to go back to the peak of our fire season in 2018," he added, in order to see the last event that "scored this high in terms of our large fire potential for our region."
The National Weather Service has issued a red-flag fire warning that will be in effect through early Wednesday east of Interstate 15 in San Diego County.
Forecasters expected the relative humidity to drop below 20% Monday afternoon and then fall as low as 5% on Tuesday and Wednesday.
Such conditions are conducive to the spread of wildfire - especially since the area has received only a fraction of its typical seasonal rainfall.
San Diego International Airport has been especially dry, recording only 0.13 inches of precipitation since Oct. 1. That's about 1.50 inches below average.
Forecasters say the county is unlikely to get appreciable rain through Dec. 15, and probably through Christmas.
California has had several rain events since early November, but the storms have largely remained in the northern part of the state. Forecast models suggest that trend could last into January.
SDG&E officials say that homeowners should bring outdoor patio furniture inside to reduce the risk of items such as chairs and umbrellas going airborne and making contact with power lines.
Affected customers should prepare for outages that could last for multiple days, especially in areas in mountain foothills, D'Agostino said.
"Damage that is seen on the electric system in many areas (is) going to require helicopters to patrol over different canyons where we can't get to it by foot" to eventually restore power, he said.