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. Offshore swells How waves are made 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. Swells There are two different types of swell that affect the surf conditions: Groundswell refers to waves generated far off of the coast. A groundswell is associated with long-period swells. Wind swell refers to waves formed from local winds to the specific surf spot. A wind swell is associated with short-period swells. 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. Swell data 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: Swell height is the height of the swell in deep water. Swell direction is the direction from which the swell is coming. It is measured in degrees (as on a compass), and often referred to in general directions, such as a NNW or SW swell. Swell period is an important factor in surf forecasting. It is a measurement of time between successive waves in seconds. If you multiply the swell period by 1.5 you will calculate the speed in knots of the wave group for deep water. Waves travel in groups, with the individual