A rainstorm is set to arrive in the Bay Area Monday and stay through Tuesday, bringing with it showers and a chance of thunderstorms that is not expected to impact the Monday morning commute but that will likely impact the evening commute, meteorologists said.
The “notable early season storm” began brewing off the Pacific Coast last week and was forecast to bring rainfall to even the Bay Area’s driest spots. The storm comes just days after federal scientists announced that La Niña has started, meaning that the waters off the coast of South American are cooler than normal and may bring drier winter weather to California.
The storm is forecast to arrive in the North Bay this morning then move into the heart of the Bay Area in the late morning and early afternoon, arriving in San Francisco around noon, said NWS meteorologist Roger Gass. The storm will continue to bring “scattered rain showers and isolated thunderstorms” through the evening and into early Tuesday morning.
“Within any heavier rain shower, there can be downpours at times, so just be mindful of water on the roadways,” Gass said. “The morning commute should be fine. We’re not seeing much in the way of rainfall right now, but the evening commute especially will be treacherous.”
Isolated showers had started in the Bay Area around 5:30 a.m., according to a social media post from the National Weather Service.
By Tuesday afternoon, the rainfall is expected to begin to dry out, Gass said.
“We really aren’t (expecting) this to be a major rain maker,” Gass added. “Being the first of the season, we would only expect nuisance flooding and very, very isolated flash flooding, but we’re not expecting any kind of flash flooding or anything like that.”
There is a 20% to 25% chance of thunderstorms across the Bay Area that could bring brief, heavy rainfall, Gass said.
“When thunder roars, go indoors,” he advised.
The rain is brought to the Bay Area by an upper-level low system coming from the Pacific Northwest coast that will pass first through the Bay Area then head down to the Central Coast, Gass added.
“It is kind of out of the ordinary, but we’ve had early season storms this early in the past,” Gass said, adding as an example that San Francisco gets about 0.94 inches of rain in October. “This amount of rainfall, will get us right about normal … for the month.”
Rainfall totals across the Bay Area from Monday to Tuesday are expected to range from half an inch in lower elevations to 2 inches in higher elevations such as the Santa Cruz Mountains, Gass said.
San Jose is projected to receive 0.75 inches of rain, while Oakland, Walnut Creek and San Francisco are all expected to receive 0.8 inches, Gass said.
The North Bay “looks to be the least winners of the rain maker,” and is forecast to receive between a quarter-inch and an inch of rainfall, Gass added.
Gass advised drivers to drive slowly and leave extra time to arrive at their destinations.
“Turn around, don’t drown,” he said. “Never drive through flooded waterways.”
This is a developing report. Check back for updates.
