That may not be a big problem if a storm is in the middle of the ocean. But if a low is near land, a 500-mile margin error may make the difference between a major swell or no waves. Furthermore, the models often predict ocean gale intensity poorly. If the wind forecast is off by 10 knots, the resulting wave forecast height will be off by 30 to 50 percent. If the swell source is 2,000 miles away, the expected swell arrival time will be a day off.
All prediction models have a hard time with tropical cyclones.
No current model is able to predict tropical cyclone formation consistently. Once a hurricane forms, the models often fail to depict the storm size and intensity correctly. The resulting wave forecast is sometimes much too high and once in a while, it is much too low. The public version of the WAM model shows only dominant swell direction. In many cases two or more swell fields are present at the same time, and the secondary swell may be the most important for surfers.