Arrifana Swell Statistics, Spring: Surf with Light or Offshore Winds
This image shows only the swells directed at Arrifana that coincided with light winds or offshore conditions over a normal 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 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 highest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the prevailing swell direction, shown by the largest spokes, was NW, whereas the the dominant wind blows from the NNW. 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 30% of the time, equivalent to 27 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal northern hemisphere spring but 11% of the time we expect swell in the range 2-3m (6.5-10ft) 11%, equivalent to (10 days). Taking into account the proportion of these swells that coincided with expected offshore winds, and given the fact that Arrifana is slightly protected from open water swells, we calculate that clean surf can be found at Arrifana about 30% of the time and that surf is messed up by onshore wind 39% of the time. This is means that we expect 63 days with waves in a typical northern hemisphere spring, of which 27 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.