San Francisco Bay & Bay Area Ocean Water Temperatures

San Francisco Bay water ranges from about 52°F in January to 69°F in August at Alameda, on the eastern Bay, based on NOAA monthly averages. The Pacific just outside the Golden Gate stays much colder, between about 52°F and 58°F all year. The table above shows the latest NOAA reading at each station, and the monthly table below shows what to expect by season.

Is San Francisco Bay Warmer Than the Ocean?

San Francisco Bay is warmer than the ocean in summer and about the same in winter, because the shallow eastern Bay heats up in the sun. Alameda averages 68.6°F in August, while the ocean 18 nautical miles west of San Francisco averages 57.2°F. In January, both sit near 52°F to 54°F.

Water temperature also changes from place to place within the Bay. Shallow, sheltered shores warm fastest, while water near the Golden Gate mixes with the cold Pacific on every tide. A reading at one station tells you about that spot, so a nearby beach can be a few degrees warmer or colder. A hot day on land does not mean the water is warm.

How Warm Is the Water in San Francisco Bay by Month?

San Francisco Bay water is warmest in August and coldest in January, according to NOAA's Coastal Water Temperature Guide. The ocean follows a different calendar, and offshore San Francisco is coldest in May, when spring winds bring cold water to the surface, and warmest in September.

These are long-term averages, so any given day can run warmer or colder. Each station also has a different length of record. Source: NOAA NCEI, Alameda (station 9414750), Richmond (9414863) and the San Francisco offshore buoy (46026), retrieved September 30, 2026.

How Cold Is the Water at Bay Area Beaches?

Water at Bay Area beaches is cold all year, usually in the 50s on the Pacific coast and the 50s to 60s inside the Bay. NOAA does not measure every beach, so each section below names the closest station and explains how the beach compares.

Ocean Beach, San Francisco

Ocean Beach water is usually in the 50s, close to the range at NOAA buoy 46026, 18 nautical miles offshore. Water at the shore can be even colder when strong northwest winds stir up cold water from below. The National Park Service advises against swimming or wading at Ocean Beach because of dangerous currents and surf, whatever the temperature.

Aquatic Park and the San Francisco waterfront

Aquatic Park is a sheltered swimming cove on the Bay, not an ocean beach. Its water usually runs from the low 50s in winter to the low 60s in late summer. NOAA's San Francisco tide station near the Golden Gate (9414290) averages 52.5°F in January and 61.5°F in September. It has not reported a recent reading, though, so it is not in the table above. For today's temperature, check the posted readings at the cove's swimming clubs.

Sausalito and Richardson Bay

Sausalito's waterfront and shallow Richardson Bay are Bay water, so they are warmer in summer than the Marin coast just outside the Golden Gate. NOAA has no station in Sausalito, so the closest Bay reading is Richmond, across the water. Shallow parts of Richardson Bay can warm a little faster on sunny days.

Rodeo Beach

Rodeo Beach faces the open Pacific, so its water tracks the offshore buoy (46026) and stays in the 50s year round. Rodeo Lagoon behind the beach is a separate body of water, and the National Park Service prohibits swimming in the lagoon. The beach itself has strong surf and sneaker waves.

Berkeley Marina

Berkeley Marina sits on the eastern Bay, where summer water is among the warmest in the region. NOAA has no station at the marina, but Alameda to the south and Richmond to the north bracket it. Their readings give a good sense of the range to expect.

Alameda

Alameda has its own NOAA station (9414750), shown in the table above. It records the warmest summer water of the stations here, with an August average of 68.6°F. The shallows at Alameda's beaches can run a bit warmer on calm, sunny afternoons.

Santa Cruz, Monterey Bay and Half Moon Bay

Santa Cruz sits on the northern shore of Monterey Bay. At NOAA's Monterey harbor station (9413450), the water averages about 55°F in winter and 59°F to 60°F in late summer. The table above also includes Monterey's offshore buoy (46042). For Half Moon Bay, the closest reading is offshore buoy 46012, 24 nautical miles out, so water at the harbor and beaches can differ. Sunny weather on land does not mean warm water.

Why Is the Pacific So Cold off San Francisco?

The Pacific off San Francisco is cold because the California Current brings cool water south from Alaska. Spring and summer winds also pull even colder water up from below, a process called upwelling. That is why the ocean can stay in the low 50s on a hot day, and why the same cold water feeds the marine layer and coastal fog. A strong El Niño can weaken that upwelling. In October 2026, as a Kelvin wave arrived, NOAA buoy 46026 off San Francisco averaged about 61°F, roughly 4°F above its October norm.

As the upwelling winds ease in late summer, the ocean surface warms a few degrees, peaking in September. For the full explanation, see why the Pacific is so cold in California.

Deep Dive: Why Does the Bay Warm So Much More Than the Ocean?

The bay and the ocean get the same summer sunshine, but the bay has far less water to warm. Most of it is shallow, much of its floor is exposed mud at low tide and the water stays in place for weeks. The ocean outside the Golden Gate is deep, well stirred and constantly refilled with cold water from below.

How Much Does Depth Matter?

U.S. Geological Survey measurements put the average depth of the South Bay at about 4.6 meters, or 15 feet, and San Pablo Bay at about 3.7 meters. Even the deeper Central Bay averages only about 13 meters. In the far South Bay, more than half the area is mudflat that drains at low tide.

By our calculation, a sunny summer day delivers enough energy to warm a 15-foot column of water by a little over 1°F. Some of that is later lost to evaporation and the night sky. The same sunshine mixed through the top 65 feet of the open ocean warms it by only about a quarter of that. Upwelling then replaces the ocean's warmed surface water with cold water from below, which the shallow bay never receives.

Mudflats add extra heat. Dark mud exposed to the afternoon sun can get much warmer than the water. When the tide returns, it floods across that warm mud and picks up heat. That is one reason the shallow edges of the bay feel so much warmer than the channels.

Why Does Bay Water Stay in Place Long Enough to Warm?

Tides move water in and out of the Golden Gate twice a day, but most of it sloshes back and forth rather than leaving. Scientists measure how long water stays in one part of the bay as its residence time. Planning studies for the South Bay salt pond restoration project describe the pattern there. Residence times are much longer in summer and in dry years, when little river water flows in.

Water that stays put for weeks keeps absorbing summer sunshine. That is why the warmest readings come from the sheltered, shallow ends of the bay, such as Alameda and the South Bay, in late summer. Near the Golden Gate, each tide brings in fresh ocean water, and temperatures stay close to those outside.

In winter the pattern evens out. The sun is weaker, the nights are long and rivers pour in cold rainwater. Shallow water loses heat as quickly as it gained it, so the bay and the ocean end up within a few degrees of each other.

Can You Swim in San Francisco Bay, and Do You Need a Wetsuit?

You can swim in San Francisco Bay, and local swimming clubs do it all year at Aquatic Park. The water is cold enough to be dangerous for unprepared swimmers, though. Cold water can trigger an involuntary gasp and rapid breathing within seconds and weaken your arms within minutes. The National Weather Service's cold-water guidance explains the risks.

Most surfers and open-water swimmers here wear wetsuits. The right thickness depends on the water temperature, how long you will be in, how active you are and your own cold tolerance. Experienced club swimmers sometimes go without one, but that takes training. A wetsuit keeps you warmer, but it does not protect you from rip currents or big surf.

Before a beach day, check the reading above, the air forecast for your destination and posted water-quality and surf notices. Our Bay Area beach day trip guide helps you pick a beach for the day. Water temperature also shapes red tides in the bay and the toxins that delay crab season. For surf safety, see rip currents at Ocean Beach.

Is It Safe to Swim in San Francisco Bay?

Swimming in San Francisco Bay is legal and can be safe if you pick the right spot and conditions. The main risks are cold water, strong tidal currents, boat traffic and bacteria after rain. Sharks are a much smaller risk than most visitors expect.

• Where to swim: Aquatic Park, the sheltered cove next to Fisherman's Wharf, is the city's main open-water swimming spot. The breakwater keeps out boat traffic and most of the current. The South End Rowing Club (1873) and the Dolphin Club (1877) have swum there for more than a century.
• Currents: Outside sheltered coves, tides move huge amounts of water through the Golden Gate, and the current can be stronger than a swimmer. Organized swims from Alcatraz are timed around slack tide, when the current is weakest. Swim outside Aquatic Park only with a club or organized event.
• Sharks: Great white sharks sometimes enter the Bay, but Shark Stewards reports no verified great white attacks on people inside it. Most sharks in the Bay are small bottom feeders such as leopard sharks.
• Water quality: Rain can wash bacteria and sewer overflows into the Bay. California's beach program advises staying out of the water during rain and for three days after. The San Francisco Public Utilities Commission tests city beaches, including Aquatic Park, and posts warnings on its beach monitoring page and the 1-877-SFBEACH hotline.

Ocean Beach is a different case, because it faces the open Pacific. Swimming there is legal but strongly discouraged because of powerful surf and rip currents, whatever the water temperature.