One of the many reasons San Diego is such a pleasurable place to sail, is our predictable wind direction and speed. When checking the weather forecast, you’ll likely see 8-10 knots from the northwest, this is known as the prevailing wind (most common). That said, San Diego will also see a southerly or easterly (Santa Ana). Let’s discuss why we see these conditions and what it means for sailors.
Prevailing Wind– As mentioned, a prevailing wind is loosely defined as a regions predominate wind direction. In San Diego, this is a northwest wind direction (Coming from the NW). This wind direction is also known as a sea breeze or onshore flow, these terms describe the wind moving from the ocean to the land.
As you have probably come to notice, the wind in San Diego builds in the late morning and weakens in the evening. This change in speed is due to the heating and cooling of both the land and ocean. The ocean, and its incredible depth, takes a long time to heat up in the sun compared to the land and its relative absorbent surfaces. Therefore, as the land heats under the morning sun, that air rises as it’s less dense, and the cooler, denser air from the ocean comes rushing in. To summarize, the cold ocean air moves to the warm land.
As the afternoon comes and goes, the land is now cooling to a temperature near that of the ocean causing a calming of the wind. If the land cools to a temperature below that of the ocean, you might see an offshore breeze, or land breeze, where a light wind now comes from the east. This is good to know when anchoring as you should prepare your boat to rotate 180 degrees and still be clear of any dangers.
Santa Ana- As you’re probably aware, Santa Ana winds are strong and dry winds coming from the southern California mountains to the coast. They normally occur in the fall months but can show up any time of year. Very dangerous for fire conditions, but for the most part a non-issue for San Diego sailors. Typically, a Santa Ana breeze dissipates as it fights the prevailing sea breeze leaving San Diego Bay with very light wind. While 10 miles east of downtown it may be blowing 15 knots from the east, the bay is likely to have 0-5 knots from the west.
That said, a strong Santa Ana can overpower the sea breeze causing large offshore waves and hazardous conditions. A southern California sailor should be aware of Santa Ana conditions if they plan to be in Catalina as waves can, and will, break in the protected anchorages of Avalon and Two Harbors.
Southerly- As the name suggest, a southerly breeze describes wind blowing from the south to the north. In San Diego specifically, a south breeze occurs when the low pressure sits to the south or west of us. As the low spins counterclockwise, the eastern side of the system blows wind from south to north. This is a somewhat rare wind direction for San Diego, but local sailors take full advantage of it as it allows you to sail from Coronado to Point Loma with minimal tacking. If timed with a trip to Catalina, a 12-hour motor just turned into an amazing 10-hour sail!
When you wake up in the morning and the deck of your boat is damp, that’s because the onshore breeze stayed on overnight and you’re likely to have a good day of sailing as the land remains hotter than the ocean. Many other factors can contribute to a wet morning, this is simply one example.
If the morning is starting off a little slow but you look east and see few clouds and a nice day, the wind is about to turn on as the land burns off the cloud layer and starts to heats up.
The two windiest parts of San Diego Bay are just inside Point Loma and the Americas Cup Harbor entrance. “The Point Loma Hurricane”, as many call it, is experienced when sea breeze comes over the top of Point Loma and rushes down the backside. Similarly, the entrance of Americas Cup Harbor (just outside the fuel dock) acts as a valley for the wind coming over Point Loma and funneling out of this channel.
Our favorite weather tool is windy.com. While it may not give the most detail for local conditions, it’s easy to navigate and useful to see the big picture. For a detailed synopsis of the southern California coast, NOOA is the best resource.