As the summer comes to a close and October rolls around, we start to see a shift in the weather pattern that produces those dry, gusty winds that blow the marine layer far out to sea, fan the flames of large wildfires, and “can” produce some fine fishing weather off the coast.
The typical Santa Ana winds pattern is shown below:
In the wake of large Pacific storms, cold air usually builds into the Great Basin (Nevada and Utah) and the circulation around the resulting center of high pressure brings wind out of the east/northeast into Southern California.
The strength of the wind depends on the strength of the high-pressure center, since all wind is the result of the atmosphere just trying to equalize things. The more out of balance the atmosphere, the more dramatic the result.
A weak-to-moderate offshore flow can often flatten out offshore seas by negating the prevailing winds, producing great weather past the Channel Islands. However, a strong Santa Ana can generate its own waves. There have been times when heavy surf has rolled into Avalon Harbor on the normally protected side of Catalina Island.
That “gradient wind” is strong enough, but when you add in the effects of the Southern California terrain, the wind actually accelerates! If you're wondering how that's possible, think about it this way: Water running through a garden hose flows at a constant rate with some pressure behind it, just like the wind blowing around the high-pressure center over the Great Basin. But what happens when you constrict the opening by putting your thumb over the end of the hose? The pressure builds and water shoots out the smaller opening you just created, as opposed to a steady stream.
The same principle (technically, it's called the Bernoulli's Principle) explains why the wind increases in speed as it is squeezed through canyons and mountain passes. The same volume of air is moving but in a smaller space, so it has to speed up!
Check out the example illustrated above showing how the winds come into play in northern Santa Monica Bay. When the wind is out of the north, it will tend to be locally stronger just below Zuma Canyon and Malibu Canyon. That is why with a Santa Ana wind forecast you'll often hear or read something like “stronger below the canyons and passes.”
So next time you feel the Santa Ana winds when you're out there fishing, you'll know what causes the wind and you can impress your fishing buddies.