Arrieta Swell Statistics, Winter: Surf with Light or Offshore Winds
The rose diagram shows only the swells directed at Arrieta that coincided with light winds or offshore conditions through a typical northern hemisphere winter. It is based on 6931 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 represent increasing swell sizes and red illustrates the 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 biggest spokes, was NNW, whereas the the dominant wind blows from the NE. 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 6% of the time, equivalent to 5 days. Open water swells exceeding >3m (>10ft) only arise 0.6% of the time in a typical northern hemisphere winter, equivalent to just one day but 5% of the time we expect swell in the range 2-3m (6.5-10ft) 5%, equivalent to (5 days). Taking into account the ratio of these swells that coincided with expected 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 6% of the time and that surf is spoilt by onshore wind 32% of the time. This is means that we expect 35 days with waves in a typical northern hemisphere winter, of which 5 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.