Bay Area to warm up rapidly. Here's where - and when - it will hit 100
The Bay Area will warm up rapidly Wednesday as a high-pressure system builds in, pushing temperatures as much as 15 degrees higher than Tuesday.
Wine Country, the southern Santa Clara Valley and cities east of the Caldecott Tunnel are forecast to surpass 90 degrees Wednesday afternoon. Vacaville could even approach 100 degrees. Oakland and downtown San Francisco will escape the most extreme heat, remaining in the 80s and 70s, respectively.
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Read more: Rip currents and sneaker waves to hit Northern California coast
The National Weather Service warns of a moderate risk of heat-related illnesses as a result of the hottest weather so far this year. Humans are more prone to suffering adverse effects from heat earlier in summer when bodies are not yet acclimated to the seasonal conditions. Elderly, children and people with underlying health conditions are most at risk of hyperthermia and heat stroke.
Unusually warm nighttime conditions will compound the shock caused by the sudden swing from drizzle to dry heat.
Temperatures are forecast to remain in the 60s Wednesday night, except at the immediate coast. Eastern Solano and Contra Costa counties may not drop below 70 degrees. Hilly areas above 500 feet, particularly above 1,000 feet, will be among the warmest places at night. These elevated nighttime temperatures are made "virtually impossible without climate change" in parts of the Bay Area, said Shel Winkley, a meteorologist at Climate Central.
These elevated nighttime temperatures, combined with an anticipated surge of gusty northeast winds, has prompted the weather service to issue a red flag warning for heightened fire danger. The warning is in effect from 11 p.m. Wednesday until 9 a.m. Thursday for the North Bay interior mountains and East Bay hills.
Thursday is forecast to be even hotter.
Triple-digit temperatures are expected along the Interstate 680 corridor in the East Bay, much of Solano County and northern portions of Wine Country. Downtown San Francisco should reach the 80s. Oakland could touch 90 degrees. San Jose should push well into the 90s, with southern portions of the city close to 100.
A heat advisory is in effect from noon to 11 p.m. Thursday for inland and bay shoreline locations, not including San Francisco.
Heat is expected to gradually ease Friday, though temperatures will remain well above normal away from the immediate coast. At the beaches, a foggy reprieve is expected Friday afternoon, lasting through the weekend.
Wednesday breakdown
San Francisco: No fog is expected in the city Wednesday morning. Temperatures should reach the 60s as early as 9 a.m., with 70-degree readings possible east of Twin Peaks by noon. The Mission District will probably be the warmest neighborhood, in the upper 70s. Elsewhere, highs will be in the upper 60s to mid-70s, except at Ocean Beach where a sea breeze should keep temperatures in the low to mid-60s.
Overnight lows are expected to be in the mid- to upper 50s in most neighborhoods, but Golden Gate Heights, Twin Peaks, Diamond Heights and Mount Davidson will probably remain in the 60s.
North Bay: Abundant sunshine is expected for what will be the hottest day of 2026 so far in many cities. Highs will be in the low to mid-90s in Santa Rosa, Napa, Sonoma, San Rafael and Fairfield. Vacaville should reach the upper 90s. Petaluma and Vallejo may remain in the mid- to upper 80s, with low 80s in Mill Valley. Bodega Bay, Stinson Beach and Muir Beach should remain much cooler, in the 60s. The sea breeze - gusting up to 15 mph - should take a slight edge off the heat in Wine Country in the evening, dropping temperatures to the 70s.
It'll be the warmest night of the year so far in many areas. Lows will be in the 50s at the coast, but the low to mid-60s in Wine Country and likely the upper 60s to low 70s in Solano County.
East Bay: A hot day and warm night is on tap. High temperatures are forecast to reach the 80s along the bay shoreline and the 90s east of the Caldecott Tunnel. The only exceptions may be the Berkeley Marina and Point Richmond where a weak bay breeze may keep temperatures in the 70s, and Antioch and Brentwood where 100-degree readings are possible.
The bay breeze should drop temperatures to the 60s in Oakland, Hayward and Fremont by 9 p.m., but it'll remain warm in the East Bay hills and the interior valleys. Overnight lows will be in the mid-60s to low 70s along the I-680 corridor and the low to mid-60s elsewhere. A dry northeast wind will pose high fire danger in the hills overnight.
Pacific Coast and Peninsula: Sunshine will dominate everywhere in San Mateo County. Daly City, Pacifica and Half Moon Bay will hold onto the cool marine air, with highs in the 60s. Elsewhere, temperatures will soar. Highs will be in the mid-70s to low 80s in San Bruno and South San Francisco and the mid-80s to low 90s in San Mateo, San Carlos and Redwood City. The sea breeze is expected to be weaker than recent days, only gusting up to 20 mph.
Overnight lows will be in the low to mid-50s at the coast and upper 50s to low 60s along the bay shoreline. Foothill communities west of I-280 may remain in the mid- to upper 60s at night, with 70s likely along Skyline Boulevard.
South Bay and Santa Cruz: Hot weather is returning to the South Bay and Santa Cruz, with forecast temperatures 10 degrees or more above normal. Highs will be in the mid- to low 90s in Palo Alto, Mountain View, Sunnyvale, Milpitas, Santa Clara and Santa Cruz and the low to mid-90s in San Jose, Cupertino, Scotts Valley, Morgan Hill and Gilroy.
A very shallow marine layer should cool off Santa Cruz and cities along the immediate bay shoreline in the late afternoon, but temperatures will be slow to drop away from the water where the breeze doesn't reach. Overnight lows are expected to remain in the 60s everywhere and the 70s above 1,000 feet in elevation.
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This story was originally published June 10, 2026 at 10:37 AM.