This image shows only the swells directed at Topsail Island that coincided with light winds or offshore conditions through a typical northern hemisphere autumn. It is based on 5144 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 illustrate increasing swell sizes and red shows the biggest swells, greater than >3m (>10ft). In each graph, the area of any colour is proportional to how commonly that size swell occurs.
The diagram implies that the most common swell direction, shown by the largest spokes, was SE, whereas the the prevailing wind blows from the NNW. 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 24% of the time, equivalent to 22 days. Open sea swells exceeding >3m (>10ft) are unlikely to happen in a normal northern hemisphere autumn but 3% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 3%, equivalent to (3 days). Taking into account the fraction of these swells that coincided with predicted offshore winds, and given the fact that Topsail Island is exposed to open water swells, we think that that clean surf can be found at Topsail Island about 24% of the time and that surf is spoilt by onshore wind 41% of the time. This is means that we expect 59 days with waves in a typical northern hemisphere autumn, of which 22 days should be clean enough to surf.
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.