This image shows only the swells directed at Traeth Lligwy that coincided with light winds or offshore conditions through a typical northern hemisphere spring. It is based on 4076 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. Green and yellow illustrate increasing swell sizes and largest swells greater than >3m (>10ft) are shown in red. In each graph, the area of any colour is proportional to how frequently that size swell happens.
The diagram suggests that the dominant swell direction, shown by the biggest spokes, was WNW, whereas the the most common 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 1.7% of the time, equivalent to 2 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal northern hemisphere spring. Taking into account the fraction of these swells that coincided with expected offshore winds, and given the fact that Traeth Lligwy is slightly protected from open water swells, we think that that clean surf can be found at Traeth Lligwy about 1.7% of the time and that surf is spoilt by onshore wind 1.3% of the time. This is means that we expect 3 days with waves in a typical northern hemisphere spring, of which 2 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.