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 CentersWhile 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.
Baron/LynxTuesday 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.
North Bay: A mild September continues in the North Bay, where high temperatures on Tuesday will be about 5 degrees below normal. Highs will range from the lower 70s near the Gulf in Marin County, mid 70s in inland Sonoma County, upper 70s in Napa County, and lower 80s in northeastern Solano County.
Some fog is possible in Petaluma, Sonoma and Napa counties before 9 a.m., but skies will likely be calm by mid-morning. Some smoke from the Northern California wildfires is expected to drift away in the afternoon and evening with only minimal impact on air quality. Expect evening gusts up to 20 mph near Delta. Overnight lows will drop to the mid 50s as fog returns to the valleys and near the Gulf.
Pacific Coast and Peninsula: The Pacific Coast has seen its share of sunshine the past few days as a low pressure system off the coast stirs up the marine layer. This low pressure will continue to swirl around, bringing periods of clouds and sun to Daly City, Pacifica and Half Moon Bay on Tuesday. A sunny period will likely be in the afternoon with highs in the mid 60s.
Near the Gulf Shore, high temperatures will be about 10 degrees higher. Gradual clearing will lead to highs in the mid-70s in Burlingame, San Mateo and Redwood City. Overnight lows in San Mateo County will drop into the mid to upper 50s with partly cloudy skies.
South Bay and Santa Cruz: Morning clouds may reach as far inland as the Santa Clara Valley on Tuesday. Any clouds will likely clear quickly for the remainder of the sunny day. High temperatures will be in the mid 70s to lower 80s in Mountain View, Cupertino, Sunnyvale and San Jose. Overnight lows will drop into the upper 50s as scattered clouds return.
Santa Cruz, Felton and Scott Valley residents may once again wake up to morning cloud cover burning off with afternoon sunshine. Some morning clouds may form as fog, limiting visibility until 9am. High temperatures will approach the upper 60s to mid 70s with lows to the mid 50s.
Contact Anthony Edwards: anthony.edwards@sfchronicle.com; Twitter: @edwardsanthonyb
