Plan your Alcatraz or San Francisco Bay open water swim with 14 years of water temperature data, and seasonal trends. Learn what to expect and how to prepare.
From 2010 to 2024, San Francisco Bay water temperatures stayed in the 50s°F, with occasional peaks into the low 60s°F during late summer and fall. We assembled 14 years of NOAA data collected near the Golden Gate Bridge, which we’ve learned to trust and confirm on our daily swims. Although the NOAA sensor stopped operating in 2024, the historical averages below remain reliable for planning open water swims in San Francisco and Alcatraz.
Average Water Temperatures in San Francisco Bay
Water temperature in the Bay shifts daily with the tides, weather, and wind. In winter, swimmers often see 1–2°F changes over a few hours as the tides change. From summer through fall, shifts of 4°F or more are common. These patterns are typical in the central Bay—between the Golden Gate Bridge and Alcatraz—where currents and wind drive constant variation.
Swimming Near Alcatraz: Temperature Guide
Detailed Temperature Breakdown
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Temp (°F) | 52.2 | 50.4 | 50.2 | 52.6 | 54.6 | 56.8 | 58.7 | 60.4 | 60.9 | 58.5 | 55.1 | 52.6 |
| Avg Temp (°C) | 11.2 | 10.2 | 10.1 | 11.4 | 12.6 | 13.8 | 14.8 | 15.8 | 16.1 | 14.7 | 12.8 | 11.4 |
Planning for Open Water Swimming in San Francisco
Swimmers preparing for an Alcatraz swim or other San Francisco open water events can expect chilly Bay waters, which average in the mid-50s°F most of the year. In central San Francisco Bay, water temperatures rarely rise above 62°F, so preparation is essential for any open water adventure.
At Pacific Open Water Swim Co., we swim year-round—24/7/365—staying acclimated and swimming skin (no wetsuits). Winter lows near 49-50°F can feel brutal, but the cold passes quickly, and a few degrees above the minimums make it manageable. Late summer and fall bring balmy 60-62°F waters for us regulars. New to San Francisco Bay’s water temperatures? Target fall through mid-November for the mildest conditions—ideal for an Alcatraz swim or open water challenge.