First ‘winterlike’ storm to hit Sonoma County, with up to half-inch of rain at higher elevations

Pummeling surf Monday presaged the arrival of much-needed rain in the first sizable storm of the season for Sonoma County, where a quarter-inch was expected Tuesday in most places and double that for higher elevations, according to the National Weather Service.

The storm front, which has been developing in the Gulf of Alaska and moving toward the West Coast, will bring intermittent showers through Wednesday, with the heaviest rain occurring between Tuesday morning and afternoon, said weather service meteorologist Brooke Bingaman.

“Winter is approaching,” Bingaman said. “This is time of year where we start to transition into more of a wet season … basically this is just the first real decent winterlike storm that we're seeing for our wet season.”

Bingaman said the storm’s coldest temperatures will come Wednesday afternoon, with highs in Sonoma County reaching only up to the low 60s. The brunt of the storm is expected to hit the Pacific Northwest, she said.

The first band of rain is expected to arrive over northwestern Sonoma County between 5 a.m. and 7 a.m., she said.

Rainfall will spread into the wider Bay Area later in the morning, about 9 or 10 a.m., she said, before reaching Central California and the Monterey Bay region Tuesday afternoon. The storm will also bring northwest winds and “gusty conditions” along the coast, Bingaman added.

The storm comes as California enters its fourth year of a severe drought. Rainfall to date for Sonoma County since Oct. 1 measures no more than 0.04 inches. Last year by this time, after a record-breaking deluge driven by an atmospheric river storm, Santa Rosa had 10.7 inches, including more than 7 inches in a single 24-hour period.

The drought has depleted the region’s two main reservoirs. Lake Sonoma is at 43%, compared to its 75% average for this time of year. Lake Mendocino is at 67% of capacity compared to its average of 80%.

The approaching storm triggered a beach hazard advisory on Monday for Bay Area residents who were planning to celebrate Halloween along the coast.

The weather service warned that the coming storm would likely cause “sneaker waves” and rip currents, particularly on northwest facing beaches up to just before midnight.

The waves, apart from the regular wind-driven ocean waves, are caused by the coming storm “pushing on the water for a longer amount of time,” creating more energy behind the swells, Bingaman said.

Bingaman said a sneaker wave occurs when wavelengths in the ocean come together and are amplified. She said sneaker waves are difficult to predict and have a longer period — the amount time between each wave.

“If you go to the beach, then it's a good idea to watch the ocean for a while,” she said. “Give it a good 20 minutes at least and see if every now and then a larger wave comes up shore and runs up the beach.”

Marin County officials also sounded their seasonal warning Monday that high tides expected over the next few months could cause flooding along shoreline communities and low-lying roads. Marin officials said data from the National Oceanic and Atmospheric Administration showed tides could be high enough to cause roadway flooding between Nov. 22-27, December 20-26, and Jan. 18-23.

“If a storm happens at the same time, it can cause tidal surges and push water levels significantly higher than predicted,” Martin officials said in a press statement.

Areas of Marin County where rising sea levels are already causing year-round tidal flooding include North San Pedro Road through China Camp in unincorporated San Rafael, Greenwood Cove Drive in Tiburon, Lucky Drive in Greenbrae, Redwood Highway at Greenbrae Boardwalk, Marin City, and the Manzanita Park & Ride lot near Tam Junction.

You can reach Staff Writer Martin Espinoza at 707-521-5213 or martin.espinoza@pressdemocrat.com. On Twitter @pressreno.

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