The theories behind wave forecasting are actually relatively simple. The difficult part is deciphering all the available and sometimes conflicting data in order to create an accurate forecast. Surf forecasters look for large areas of strong wind blowing over water in the direction of the area for which they wish to create a prediction. This wind usually comes in the form of storms. Forecasters find these storms using a combination of real-world data such as ship reports and weather buoy readings, and weather maps of the current ocean wind speeds and swell data.
More fetch equals more wave energy transmitted to the water in the form of waves.
If a lot of wind blows over a long fetch in the direction of, say, the North Shore of Hawaii, for a long enough time, the result will be waves. To determine if or when those waves will hit a particular spot, forecasters look for several pieces of critical information about the swell. Here's an example of how you might predict waves at your own local surf break in, let's say, Hawaii. For the sake of simplicity, assume the swell is traveling directly toward you. The rate of travel for a 14-second interval is 550 miles per day.