What happened to “Second Summer” in San Francisco? Here’s what comes next

September has passed the halfway mark in San Francisco, and what many know as “the second summer” has disappeared from the city.

The average daytime high temperature during the first 17 days of September was 68.3 degrees in San Francisco, just below the 30-year September normal of 70 degrees. The warmest day reached only 72 degrees, and came on the second of the month. Santa Rosa, Napa, Oakland and Concord recorded similar trends, with maximum temperatures averaging 1 to 3 degrees below normal.

High temperatures remained on the cool side during September across the Bay Area, being a few degrees below normal for most cities.

NOAA Regional Climate Centers

While daytime temperatures remained on the cool side, nighttime was a different story.

Above-normal water temperatures in San Francisco Bay and the Pacific Ocean kept nights warm. During the first 17 days of September, the average overnight low temperature in Auckland was 57.8 degrees, more than two degrees above normal.

Forecast end of September

Extreme heat reminiscent of recent Septembers in 2019, 2020 and 2022 have avoided the Bay Area this month, and the forecast remains unfavorable for hot temperatures in the near future.

For the rest of the week, high temperatures will continue to stay on the cool side, in the mid 60s on the coast, dropping to the mid 70s near the Gulf and dropping into the 80s inland, about 3 to 5 degrees below normal. Nighttime temperatures will gradually trend lower during the week, from the upper 50s Tuesday night to the mid 50s Friday night.

Forecasts from the Climate Prediction Center do not indicate much change by next week. The forecast favors near-normal temperatures during the last week of September — 60s on the coast, 70s near the Gulf, and low 80s inland.

The Climate Prediction Center's 8- to 14-day forecast favors near-normal temperatures for most of the Bay Area.

The Climate Prediction Center’s 8- to 14-day forecast favors near-normal temperatures for most of the Bay Area.


Tuesday collapse

San Francisco: Intensifying northwesterly winds along the coast mean morning clouds are likely to be more widespread on Tuesday morning than on Monday. The weak front should help clear the clouds around the city by a mostly sunny mid-morning to late afternoon.

High temperatures will range from the mid 60s in Ocean Beach to the upper 60s in Rossin Hill to near 70 degrees in Mission, Potrero and South Market counties. Expect wind gusts of 20 mph in the afternoon near Golden Gate, Twin Peaks and other wind-prone locations. Overnight lows will drop into the upper 50s as clouds pass through.

East Bay: A mostly cloudy morning near the Gulf Shore will dampen daytime highs, with temperatures a few degrees cooler than Monday. Temperatures in Richmond, Berkeley, Oakland and Alameda will peak in the upper 60s to near 70 degrees under sunny afternoon skies.

Scattered morning clouds are expected on Interstate 680 between Martinez and Dublin. The clouds will burn through on a clear afternoon with temperatures reaching the upper 70s.

Overnight lows around the East Bay will drop into the upper 50s as patchy clouds return to the Gulf Shore.

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