This image shows only the swells directed at Pors Carn that coincided with light winds or offshore conditions through a typical August. It is based on 1736 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. Green and yellow show increasing swell sizes and largest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the dominant swell direction, shown by the biggest spokes, was W, whereas the the most common wind blows from the WNW. 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 34% of the time, equivalent to 11 days. Open water swells exceeding >3m (>10ft) only arise 1.8% of the time in a typical August, equivalent to just one day but 14% of the time we expect swell in the range 2-3m (6.5-10ft) 14%, equivalent to (4 days). Taking into account the fraction of these swells that coincided with expected offshore winds, and given the fact that Pors Carn is slightly protected from open water swells, we estimate that clean surf can be found at Pors Carn about 34% of the time and that surf is blown out by onshore wind 19% of the time. This is means that we expect 16 days with waves in a typical August, of which 11 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.