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Forecasters are warning Bay Area residents to brace for a significant and unusually early rain event this weekend.
With the heaviest rainfall expected from Sunday into Monday, the so-called “atmospheric river” could bring up to 9 inches of rain to some elevated parts of the region.
According to Brooke Bingaman, lead forecaster at the National Weather Service, these rainstorms are typical for the area, which experiences an average of 5 to 7 atmospheric rivers per year. But she said this one is unusual in that “it's happening so early in our wet season.”
Forecasters said the rain coming through Thursday night into Friday afternoon will affect the north bay more than other parts of the Bay Area, with areas south of the Golden Gate Bridge not expected to get more than a half-inch of rain from the storm.
Southerly winds of 23 mph with gusts up to 47 mph could blow through the Redwood City region, according to the weather service.
However, the most severe storm will come this weekend, with the atmospheric river possibly bringing 6 to 9 inches of rain in areas like the north bay mountains and up to 3 inches in other parts of the region. Forecasters expect three-quarters to 1 inch of rain in Redwood City on Sunday, with a possible thunderstorm after 11 p.m.
An atmospheric river is “a concentrated plume of moisture that travels across the Pacific Ocean and then makes landfall somewhere along the west coast,” according to Bingaman. She added that, unlike a regular winter storm, an atmospheric river is named for its characteristic “river of continual moisture” that hits the same area for a sustained period of time.
Jonathan Cox, deputy chief of Cal Fire's San Mateo Division, said Friday that rainy weather coming through the region this past week has helped quell immediate concerns over any new major wildfires starting and "is very welcome for a lot of reasons."
However, the burn scars from the CZU Lightning Complex fires in San Mateo and Santa Cruz counties last year are among the areas at risk of debris flows and flash floods, as the larger storm descends on the region this weekend.
Though urban areas like Downtown Redwood City are less susceptible to debris flows from wildfire burn scars, Bingaman warned that flooding is still possible.
“Our concern for the more populated areas is that, with all the concrete, the water can't get absorbed by the soil,” she said, adding that people should avoid driving through any flooded roadways. “It’s easier for water to start ponding in urban areas, and that could happen very rapidly.”
Forecasters said the weather system is still too far away to make more exact predictions but are advising people to stay in touch with local media outlets, sign up for wireless emergency phone notifications, and tune into the radio or social media.
“On Sunday that’s when you need to be the most alert about what’s going on with the weather in your area,” said Bingaman
Cal Fire and other first responder agencies in the two counties are encouraging people to check Zonehaven, a platform that helps communicate real-time evacuation information to the public and divides areas into evacuation zones. People can look up their address to find out their zone at https://community.zonehaven.com/.
Along with knowing their evacuation zone, Cox recommended that people in both San Mateo and Santa Cruz counties sign up for their respective county's emergency alert systems to receive text or voice messages in the event of an emergency.
San Mateo County residents can sign up for SMC Alert at https://hsd.smcsheriff.com/smcalert and Santa Cruz County residents can sign up for CodeRED, their agency's alert system, at https://www.scr911.org/.
The major weather system this weekend will also bring major waves along the coast, with swells as high as 20 to 30 feet coming starting Sunday and peaking Monday into Tuesday, according to the weather service.
As a result, agency officials said a high surf advisory or warning could be issued as soon as Friday, and people are advised to keep an eye out for rip tides and sneaker waves as well as hazardous conditions for small vessels on the water.
Bay City News contributed to this report.
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Leah Worthington is the lead reporter at the Redwood City Pulse, a local news site dedicated to providing accurate and timely news to the Redwood City community. Leah can be reached at lworthington@rwcpulse.com, on Twitter, and by phone at 650-888-3794. To read more stories about Redwood City, subscribe to our daily Express newsletter on rwcpulse.com.
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