Statistiques de Houle pour Arrieta, Printemps: Vagues avec Vents Légers ou Favorables.
This image shows only the swells directed at Arrieta that coincided with light winds or offshore conditions through a typical northern hemisphere spring. It is based on 6580 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 show increasing swell sizes and red represents largest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how frequently that size swell was forecast.
The diagram suggests that the most common swell direction, shown by the biggest spokes, was NNW (which was the same as the most common wind direction). 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 4% of the time, equivalent to 4 days. Open sea swells exceeding >3m (>10ft) are unlikely to occur in a normal northern hemisphere spring but 4% of the time we expect swell in the range 2-3m (6.5-10ft) 4%, equivalent to (4 days). Taking into account the fraction of these swells that coincided with predicted offshore winds, and given the fact that Arrieta is quite sheltered from open water swells, we think that that clean surf can be found at Arrieta about 4% of the time and that surf is messed up by onshore wind 27% of the time. This is means that we expect 28 days with waves in a typical northern hemisphere spring, of which 4 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.