This image shows only the swells directed at Cap Ferret that coincided with light winds or offshore conditions through a typical December. 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 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 often that size swell happens.
The diagram indicates that the prevailing swell direction, shown by the largest 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 35% of the time, equivalent to 10 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal December but 8% of the time we expect swell in the range 2-3m (6.5-10ft) 8%, equivalent to (2 days). Taking into account the fraction of these swells that coincided with predicted offshore winds, and given the fact that Cap Ferret is exposed to open water swells, we calculate that clean surf can be found at Cap Ferret about 35% of the time and that surf is blown out by onshore wind 58% of the time. This is means that we expect 28 days with waves in a typical December, of which 10 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.