This image shows only the swells directed at Topsail Island that coincided with light winds or offshore conditions through a typical northern hemisphere summer and is based upon 5066 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. Green and yellow represent increasing swell sizes and red shows highest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the most common swell direction, shown by the largest spokes, was SE, whereas the the dominant wind blows from the SSW. The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 16% of the time, equivalent to 15 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal northern hemisphere summer. Taking into account the ratio of these swells that coincided with forecast offshore winds, and given the fact that Topsail Island is exposed to open water swells, we estimate that clean surf can be found at Topsail Island about 16% of the time and that surf is spoilt by onshore wind 49% of the time. This is means that we expect 59 days with waves in a typical northern hemisphere summer, of which 15 days should be surfable.
IMPORTANT: Beta version feature! Swell heights are open water values from NWW3. There is no attempt to model near-shore effects. Coastal wave heights will generally be less, especially if the break does not have unobstructed exposure to the open ocean.