Arrifana Swell Statistics, Agosto: Surf with Light or Offshore Winds
This image shows only the swells directed at Arrifana that coincided with light winds or offshore conditions through a typical August and is based upon 2480 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 represents the biggest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how frequently that size swell occurs.
The diagram suggests that the dominant swell direction, shown by the longest spokes, was NW, whereas the the prevailing 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 23% of the time, equivalent to 7 days. Open sea swells exceeding >3m (>10ft) are unlikely to happen in a normal August but 21% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 21%, equivalent to (7 days). Taking into account the ratio of these swells that coincided with forecast 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 23% of the time and that surf is messed up by onshore wind 20% of the time. This is means that we expect 13 days with waves in a typical August, of which 7 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.