Surf forecasting

Surf forecasting is the process of using offshore swell data to predict onshore wave conditions. It is used by millions of people across the world, including professionals who put their forecasts online, meteorologists who work for news crews, and surfers all over the world. It is impossible to make an exact prediction of the surf (shape and size of breaking waves), but by knowing a few factors a good prediction can be made. One needs to have an understanding of how waves are formed, a basic knowledge of bathymetry, and information (such as tides, location, and weather) about the surf spot being forecasted to accurately forecast the surf.

Waves are created as wind blows over the ocean, transferring its energy into the water. The size of the swell is affected by three variables: the velocity of the wind, its duration, and its fetch, or distance the wind blows over.

There are two different types of swell that affect the surf conditions:

In general groundswell produces waves that are much better for surfing. Wind swell is usually smaller, and almost always choppier and harder to surf than groundswell. Although both are present at most surf spots, groundswell creates much better breaking waves and dominates the lineup. This distinct separation occurs because groundswell originates far from the shore and has more time to separate into organized patterns, which are much easier to surf.

In order to forecast the surf, there is important data from the swells that need to be analyzed. There are three main factors used in surf forecasting:

These three pieces of information are the main key to forecasting the surf. If there is a swell of significant height that is headed in the direction of the break you are forecasting for, then there probably will be good surf. The swell period will tell you how much a swell will wrap into a spot and how much it will grow in deep water.

One important fact about waves is that they focus more of their energy towards shallower water. Waves will always turn and refract towards shallower water. This is where swell period can drastically affect the conditions. The longer the period of the swell the more it tends to wrap into a spot. This means that a swell might cause waves in a spot even if it is not directed at the spot. Significant underwater irregularities, such as underwater canyons and sea mounts, can also affect how the waves come into a surf spot. Irregularities like these may cause the surf to be much larger at one spot, while almost nonexistent at another nearby. This is the case at surf spots such as Black's Beach, El Porto, and Mavericks.

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