San Francisco Bay Area’s hottest day of 2025 is here despite the start of the fall; temperature may hit low 100 degrees

Fall arrived in the San Francisco Bay Area on Monday (September 22, 2025), but the forecast in the region shows a different picture. Temperatures across the Bay Area are likely to peak on Tuesday (September 23, 2025). According to the San Francisco Chronicle, some coastal regions possibly reach 90 degrees, and inland areas climb into the low 100s.

Fire weather risk will increase across the region due to a period of offshore winds on Monday and Tuesday. Mercury will rise at the start of the week, with some of the hottest temperatures of the year possible on Tuesday, the San Francisco Chronicle reported.

After two hot days at the start of the week, things will settle down a bit as showers accompanied by thunderstorms are likely on Wednesday (September 24, 2025). In the later part of the week, sunny skies and high mercury ranging in the 70s and 80s are expected from Thursday onward.

The Bay Area to feel the heat

The Bay Area will witness a hot start to the week with temperatures rising up to 80 degrees on Monday and Tuesday, with Tuesday having the potential to be the warmest day so far this year for San Francisco. At the beginning of the week, there is a small ridge of high pressure in the north of an offshore cutoff low-pressure system.

According to the San Francisco Chronicle, the tiny bump in the atmosphere will pin the low in place and make way for warm, dry air to blanket California. When it happens, it will result in a classic offshore wind pattern with sinking air above. Also, the weak winds out of the east will flatten the marine layer and let heat spill all the way to the coast.

The signal is specifically strong on Tuesday. The upper-air temperatures will be 3 to 6 degrees higher than usual for late September, and the marine layer is unlikely to rebuild overnight on Monday. With all this likely to happen, the Bay Area is bracing for one of its hottest days of the year on Tuesday. San Francisco will probably top out at 90 degrees. On the other hand, the usual interior hot spots surge into the upper 90s and low 100s.

Besides the temperature, the fire weather risk will also increase with a 24- to 48-hour period of offshore winds likely from Monday through Tuesday, the San Francisco Chronicle reported.