This image shows only the swells directed at Cap Blanc Nez that coincided with light winds or offshore conditions through a typical January. It is based on 1240 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 illustrate increasing swell sizes and red illustrates highest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the prevailing swell direction, shown by the largest spokes, was NNE, whereas the the dominant wind blows from the SW. 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 8% of the time, equivalent to 2 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal January. Taking into account the fraction of these swells that coincided with expected offshore winds we calculate that clean surf can be found at Cap Blanc Nez about 8% of the time and that surf is spoilt by onshore wind 26% of the time. This is means that we expect 11 days with waves in a typical January, 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.