How the coming rain storm compares to the past

Wet weather is on tap for the Bay Area this weekend, as a storm barrels toward California from Alaska. Though unusual, it’s not unprecedented to see rain in San Francisco at this time of the year.

“To see rain at all in September is not that uncommon,” said Dalton Behringer, a meteorologist with the National Weather Service’s Bay Area office. “But to see this much rain in September is a little more on the rare side of things.”

Three-quarters of an inch of rain is expected in the South Bay. Some mountainous areas could see more than two inches.

But will the storm totals surpass all-time records in San Francisco and surrounding areas?

Probably not. But it could still be the wettest month in decades.

The Golden Gate Bridge reflected in raindrops on Christmas Day last year.

The Golden Gate Bridge reflected in raindrops on Christmas Day last year.

Stephen Lam/The Chronicle 2021

Meteorologists are forecasting about an inch of rain in downtown S.F. This could make this month the wettest in more than 30 years – since September 1989 – when 0.98 inches of rain fell. The all-time September record for the city goes back to 1904, which saw a staggering 5.07 inches of rain.

We’re not likely to see any daily records drop either.

“The bulk of the rain will be Sunday to the end of Monday morning,” Behringer said. “But then lingering spotty showers through the day Monday and into Tuesday morning.”

For downtown San Francisco, the record for Sept. 18 — the date this Sunday — is 2.01 inches, set in 1959. The record for September 19 is 0.83 inches, set in 1977.

“Those daily records may actually be a little tough to beat,” Behringer said.

Other parts of the Bay Area are expected to see more precipitation.

“Really the winner for this one is going to be North Bay,” Behringer said. “They are going to get most of what we’re going to see — particularly coastal, higher terrain.”

The Sonoma Coast could see upward of 2 inches of rain. In Santa Rosa, around 1.5 inches to inches of rain is expected.

This isn’t expected to break any monthly records and daily records may be out of reach too. The daily record for September 18 is 2.82 inches, set in 1959. That same year saw a record 0.34 inches of rainfall on September 19.

“Depending on if the rainfall lingers into Monday for Santa Rosa, that record could be in jeopardy,” Behringer said. “But with the bulk of the rain on Sunday, it’s going to be hard to break that record for Santa Rosa as well.”

Jack Lee (he/him) is a San Francisco Chronicle staff writer. Email:

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