Second Summer: Why was an excessive heat warning issued for San Francisco?

Temperatures in San Francisco rose to 94 degrees on Tuesday, prompting authorities to issue an excessive heat warning through Thursday. Residents are advised to visit cooling centers and public swimming pools or take advantage of free ferry rides offered on Wednesday. Temperatures were even higher inland, exceeding 100 degrees in some places.

The intense heat is expected to continue until Thursday, with persistent high temperatures forecast through the weekend.

Inland areas near San Francisco experienced even more extreme heat this week. Santa Rosa recorded 102 degrees Tuesday, while San Rafael hit 105 and San Jose hit 100 degrees. According to the National Weather Service (NWS), all three cities broke the previous Oct. 1 records set during a 1980 heat wave.

The NWS reissued its Excessive Heat Warning and Warning on Wednesday, effective from 11 p.m. Wednesday through 11 p.m. Friday. This advisory affects regions such as the inland and coastal areas of the North Bay, San Francisco, the East Bay, the South Bay and the Santa Cruz Mountains.

Inland, temperatures could rise to 108 degrees, while downtown San Francisco could reach 87 degrees. Temperatures could rise to 95 degrees in coastal areas of the North Bay, Peninsula and Monterey Bay.

The NWS advises the public not to leave people or pets in vehicles during this fall heat wave, limit outdoor activities during peak heat, stay hydrated, and take cool-down breaks.

Why is San Francisco experiencing a heat wave now?

The heat wave is driven by offshore winds that push hot air from inland regions towards coastal areas. Normally, San Francisco stays cooler due to a marine layer caused by sea breezes, but this wind pattern has temporarily reversed.

Other parts of California are also experiencing above-average temperatures due to a heat wave in the Southwest. Officials warn that the dry heat has increased the risk of wildfires, with 1 million hectares of land already burned this season.