A supermoon — the closest such moon to the Earth this year — is wreaking havoc with ocean tides up and down the state’s coast just as an atmospheric river storm moved through Northern California.
The “Beaver Moon” has brought with it king tides. And forecasters say that Southern California could see dangerous rip currents and an increased risk of drowning from large breakers, as well as the chance of coastal flooding over the next two days.
But the Southland will largely be spared the rain that has inundated some areas of Northern California in a storm strong enough that the state dispatched emergency services personnel in two counties.
The National Weather Service office in Sacramento was forecasting the heaviest downpours in three areas, where the rain was expected to continue into Thursday afternoon. Two to three inches of precipitation was expected in Blue Canyon in the Tahoe National Forest, Quincy in the Plumas National Forest and Sims in the Shasta-Trinity National Forest.
San Francisco and Sacramento expected up to half an inch of rain from Wednesday into Thursday, while Santa Rosa was expecting between a half and a full inch.
The rain, which began Tuesday, is expected to continue until Friday around 9 or 10 a.m., according to Sacramento meteorologist Sara Purdue. Commutes are expected to be affected, with slick roads and water ponding on roadways, according to the weather service.
The heaviest rain probably has already fallen, according to Purdue, “though light rain is expected to linger in Shasta County and nearby areas through Thursday and into Friday” morning.
Meanwhile, November’s supermoon was causing some flooding. The phenomenon is referred to as the “Beaver Moon” because it’s a time when beavers build their dams and take shelter before the ground freezes, according to the Farmers’ Almanac.
The slightly oval shape of the moon’s orbit brings it closer to Earth at certain times of the year, when it covers a slightly larger area of the sky, according to the Griffith Observatory.
“Sometimes the full Moon occupies the closest point of its orbit, and that is a so-called ‘supermoon,’” according to the observatory.
The supermoon, which was at it peak brightness on Tuesday and Wednesday at 5:19 a.m., was 221,817 miles from Earth, according to the Farmers’ Almanac. Its proximity does affect ocean tides, and king tides are forecast to peak Thursday along the coast.
“If you were in outer space looking at the planet, you’re going to see a slight bulge in water on one side of the planet,” said Matt Mehle, a meteorologist at the National Weather Service’s Monterey office. “So we end up with a slightly higher tide as a result of that.”
Consequently, there’s a high-surf impact warning from the Central Coast to Los Angeles County. There is also an increased risk of drowning from large breakers, strong rip currents and dangerous waves on rocks through Saturday, according to the National Weather Service’s Oxnard office.
Peak surf is expected to hit 12 to 18 feet in the Central Coast, 8 to 12 feet in Ventura County and 5 to 8 feet in Los Angeles and Santa Barbara counties.
Farther north, the National Weather Service issued a coastal flood advisory Tuesday that’s in effect through Saturday. The advisory spans from Sonoma County to Monterey County and includes San Francisco’s shoreline.
As of Wednesday afternoon, Coyote Creek, which flows through the Santa Clara Valley, was seeing some minor flooding due to the high tide tidal surge, according to the weather service.
Farther up the coast, heavy rains were expected Thursday in Del Norte County, which borders Oregon, and Humboldt County, directly below it. The two counties were also under a coastal flood advisory.
Gasquet, along Highway 199, was hit with just over half an inch of rain on Wednesday, with a total of about 2½ inches expected by Friday morning. Klamath is also expected to receive 2 inches.
Gov. Gavin Newsom said Tuesday he would be pre-deploying specialized emergency crews to protect communities in Del Norte and Humboldt counties.
That help included 32 fire personnel and nine fire engines through Thursday evening.
“These efforts ensure that resources are ready to respond quickly, minimizing the potential impact of mud and debris flows, and potential flash flooding,” Newsom said in a release.
The governor’s office was advising drivers to stay off the roads, if possible, and never to walk or drive through floodwaters.
“For this storm, the dividing line is the Golden Gate Bridge,” National Weather Service Monterey meteorologist Ryan Walbrun said. “In the North Bay, you have up to 2½ inches and you’re seeing rain in Marin and Napa counties, which is what we expected. Then it tapers off below.”
Although there have been some coastal flood advisories for Lompoc and Santa Barbara, rain had been light as of Wednesday night.
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