The Central Bay of San Francisco is known throughout the sailing world as one of the grandest of all places to sail.
Cool winds, often blowing at 20 mph or more through the Gate, can drop summer temperatures on the Bay into the 50s. Bay sailors come out to play while inland temperatures remain at over 100 degrees. Photo courtesy of OCSC.
By Captain Ray
Published: July, 2008
The Central Bay is bounded on the south by the city front and Treasure Island and on the north by Angel Island and its lee. It extends west to east from the Golden Gate Bridge all the way across to the flats of Berkeley, a distance of eight nautical miles. Sailors often refer to this area as The Slot. Not only are the views spectacular, but here the wind is consistently strong for six (and sometimes even seven) months of the year.
During a good year, lucky San Francisco Bay sailors will have winds that blow 20 knots or more almost every afternoon from April through October. As you can see on your beautiful ferry ride home in the afternoon this summer, these strong steady and dependable winds have returned. Although winds of this strength are sometimes intimidating to those unfamiliar with them, for skilled and experienced San Francisco Bay sailors they bring great joy. And it’s not just the winds’ speed that elates Bay sailors; it’s also their predictability. There are very few places on Earth where winds of this velocity are so consistent.
This San Francisco Bay summer wind is the result of a unique geographical phenomenon. At 38˚ north of the Equator, the Bay Area is in the path of the prevailing westerlies. This means that most of the time the wind comes from the west. Just 60 miles inland from the Bay is the Great Central Valley, with its extremely high summer temperatures. From Bakersfield in the south to Redding in the north, afternoon summer temperatures often reach 110˚F and sometimes even higher. This is the only place on earth that I know of where you can have a 50˚F temperature difference within 50 miles, without any elevation change. It can be 55˚F in San Francisco and, at the same time, 105˚F in Vacaville.
As this very hot air rises, cooler air is pulled in to replace it. The hotter the afternoon temperature in the Central Valley, the more rapidly the heated air rises and the stronger the inward air flow. The Sierra Nevada Mountains, a 10,000 foot wall to the east, make it unlikely the replacement air will come from that direction. There are, however, many low places between the Central Valley and the Pacific Ocean through which this inrushing air can pass easily. Only the Golden Gate, however, goes all the way down to sea level. Because of this, the Gate is the funnel for the primary source of replacement air for the Central Valley. Since air is fluid, it accelerates as it is forced to squeeze through narrow openings. As this cooler replacement air squeezes through the Golden Gate, it is accelerated directly down ‘The Slot, setting up the Bay’s exhilarating winds of summer.
Ray Wichmann, is a US SAILING-certified Ocean Passagemaking Instructor, a US SAILING Instructor Trainer, and a member of US SAILING’s National Faculty. He holds a 100-Ton Master’s License, was a charter skipper in Hawai’i for 15 years, and has sailed on both coasts of the United States, in Mexico, the Caribbean, and Greece. He is presently employed as the Master Instructor at OCSC Sailing in the Berkeley Marina.
