On the central coast of California, about 120 km (75 miles) south of San Francisco, Monterey Bay is a broad bay of the Pacific Ocean that curves from Santa Cruz in the north to Monterey and Pacific Grove in the south. At its centre, off Moss Landing, begins the Monterey Canyon, a submarine canyon that runs 153 km out to sea with walls about 1.6 km high. The bay lies within the Monterey Bay National Marine Sanctuary, designated on 18 September 1992, which covers 15,783 km² (6,094 sq mi) of ocean along 444 km (276 mi) of shoreline, from Marin County just north of the Golden Gate to Cambria. Its year runs on a sharp wet–dry rhythm. Monterey averages 435 mm (17.11 in) of rain, almost all of it between October and April, while summer brings fog and cold upwelled water instead. Local records count rainfall by the “rain year” from July to June, and this guide follows the bay through that year, month by month.
July to September: Fog, Upwelling and Almost No Rain
The rain year opens in its driest stretch. Monterey’s 1991–2020 normals give just 0.02 in (0.5 mm) in July, 0.09 in in August and 0.08 in in September. The sea, not the sky, sets the weather. Along this coast the prevailing northwesterly winds push surface water offshore through the Ekman effect, and cold water from below rises to replace it. This upwelling cools the already chilly California Current and is the mechanism behind California’s summer coastal fog. It also lifts nutrients into the sunlit surface, feeding the plankton at the base of the bay’s food web. The California Current is one of six major coastal currents in the world associated with strong upwelling, alongside the Humboldt, Canary, Benguela, Oyashio and Somali currents.
Monterey lies at roughly the same latitude as Death Valley, yet summer days are cool and often grey, and its highest average high, in September, is only 68.2 °F (20.1 °C). Average sea-surface temperature in the sanctuary is about 13 °C (55 °F). Well-fed water supports at least 36 species of marine mammals, 94 of seabirds and 525 of fish, as well as four species of sea turtle and some 450 species of marine algae. Late summer is also the peak of sea otter mating in California, which runs from July to October. Protecting this productivity took decades: the California Coastal Commission recommended a sanctuary in 1975, the Reagan administration dropped the area from consideration in 1983, and when Congress revived the idea in 1988, public hearings shaped by memories of the 1969 Santa Barbara oil spill pushed for a larger area. Offshore oil drilling and seabed mining are now banned throughout.
October to Mid-November: First Rains and the Old Sardine Season
October brings the first real rain, about 0.83 in (21 mm) on average, followed by 1.64 in (42 mm) in November. For half a century this was also when Monterey went back to work. Sardines ran in the bay from October to February. When the boats came in loaded, each cannery’s whistle called its workers to the line for 12- to 15-hour shifts, and there was little work from March to September. Canning began in 1902, when Frank Booth bought a failing cannery on Fisherman’s Wharf. In 1914 demand surged after France suspended sardine exports during the First World War. Sicilian fishermen led by Pietro Ferrante brought the Mediterranean lampara net, and the Norwegian engineer Knut Hovden built an assembly-line canning system in 1913.
By the early 1940s about 30 canneries and reduction plants lined Ocean View Avenue, which was officially renamed Cannery Row in 1958 after John Steinbeck’s 1945 novel. After the Second World War the sardine population collapsed and the fish vanished from the bay within a few years. The canneries closed one by one, the last of them, Hovden, in 1973. In October 1984 the Monterey Bay Aquarium opened on the Hovden site, the first aquarium to show a living kelp forest; our guide to kelp forests explains why those giant algae thrive in cold, upwelled water like the bay’s.
Mid-November to February: The Davidson Current, Storms and Pups on the Beaches
In winter the ocean turns over. Between mid-November and mid-February the northerly winds weaken and give way in part to southwesterlies, and the Davidson Current, a countercurrent that flows north along the coast at around 200 m depth all year, rises to the surface beside the shore. It is named after the geodesist George Davidson of the early California Academy of Sciences. This is also the heart of the rain year: December averages 2.86 in (73 mm), January 3.45 in and February 3.46 in (88 mm). Snow in Monterey itself is extremely rare. A light coating fell in January 1962, February 1976 and December 1997, and 3.2 in (8.1 cm) fell in March 2006, while the Santa Lucia and Gabilan ranges above the bay sometimes turn white. The bay’s name is itself a winter one: Sebastián Vizcaíno sailed in on 16 December 1602 and called it Puerto de Monterrey after the Count of Monterrey, viceroy of New Spain.
The beaches fill with animals at the same time. Northern elephant seal bulls return to their breeding beaches in December and January, ahead of the females, which give birth and nurse their pups for about four weeks. At Año Nuevo, on the sanctuary coast north of Santa Cruz, no elephant seals were seen at all until 1955. The first pup was recorded in the early 1960s, and thousands are now born there every year. The colony faced a new threat in February 2026, when highly pathogenic avian influenza (H5N1) was confirmed in pups at Año Nuevo; the state park closed until 11 April 2026, reopening once pup deaths fell. In southern sea otter populations, births peak between January and March. Elkhorn Slough, the tidal estuary that meets the bay at Moss Landing, has the greatest concentration of sea otters in California.
Flood Years and Dry Years on the Pajaro and Salinas Rivers
Two rivers carry the winter rain into the bay, and both swing between flood and drought. The Pajaro River drains about 3,400 km² (1,300 sq mi) and reaches the sea west of Watsonville, forming the whole boundary between Santa Cruz and Monterey counties. The towns of Pajaro and Watsonville stand on its natural floodplain. Levees built by the Army Corps of Engineers in 1949 have failed or been overtopped several times since, and the town of Pajaro flooded badly in 1995, 1998 and 2023. During the 2022–23 California storms the Pajaro levee failed on 10 March 2023, forcing nearly 2,000 residents to evacuate. A second breach was found on 13 March. Experts blamed poor construction materials, earthquakes and burrowing rodents, and the 1989 Loma Prieta earthquake had already deformed the levee system.
The Salinas River, the longest river on the Central Coast at 282 km (175 mi), enters the bay about 8 km south of Moss Landing. It flowed all year until 1989. Its lower reaches then dried out completely from 2013 to 2016, mainly because of farm water demand and falling water tables, until the drought-breaking rains of January 2017 restored the flow. In 20th-century flood years, which came roughly every three to ten years, it could spread more than a mile wide. Its mouth has also moved: winter storms in 1909 shifted it to its present position south of Moss Landing.
Rain years differ enormously from one to the next. Combining the Monterey records, the wettest rain year was July 1997 to June 1998, with 47.15 in (1,198 mm), almost three times the average. That was an El Niño winter, and it included the wettest single month on record, February 1998, with 13.73 in (349 mm). The same El Niño may have killed about 80% of that season’s elephant seal pups. The driest rain year, July 2013 to June 2014, brought only 7.67 in (195 mm), in the middle of the years when the Salinas ran dry. Our guide to El Niño weather patterns explains why the central Pacific can swing a California winter so far.
March to June: The Rains Fade and the Northwesterlies Return
March still averages 2.89 in (73 mm) of rain, but April drops to 1.15 in, May to 0.50 in and June to just 0.14 in. As the storms ease, the northwesterly winds strengthen again, upwelling builds towards its summer peak, and the cycle that began in July closes. Elkhorn Slough shows the turn of the seasons well. It is a 7-mile (11 km) tidal slough, California’s second-largest estuary and the first estuarine sanctuary in the United States, and it has been a Ramsar wetland of international importance since 2018. More than 340 species of birds have been recorded there, among them seasonal flocks of migrating shorebirds. Offshore, the bay lies on the migration path of gray and humpback whales, and killer whales follow the coast to hunt the gray whales as they move north.
Below all of this the canyon keeps its own slow calendar. Monterey Canyon’s deepest point inside the sanctuary is 3,884 m (12,743 ft), deeper than the Grand Canyon. Geologists think it may be the old outlet of a much larger river that once drained the Central Valley, and that it has since been carried northwest along the San Andreas Fault. Among the world’s submarine canyons, few sit so close to shore, and this one is the deep, cold engine whose upwelled water makes the bay’s dry summer as productive as its wet winter.