Asilomar Swell Statistics, Summer: Surf with Light or Offshore Winds
This image shows only the swells directed at Asilomar that coincided with light winds or offshore conditions over a normal northern hemisphere summer. It is based on 7266 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. Green and yellow represent increasing swell sizes and red illustrates biggest swells greater than >3m (>10ft). In each graph, the area of any colour is proportional to how commonly that size swell was forecast.
The diagram implies that the dominant swell direction, shown by the largest spokes, was W (which was the same as the prevailing 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 22% of the time, equivalent to 20 days. Open sea swells exceeding >3m (>10ft) are unlikely to occur in a normal northern hemisphere summer 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 Asilomar is exposed to open water swells, we calculate that clean surf can be found at Asilomar about 22% of the time and that surf is messed up by onshore wind 52% of the time. This is means that we expect 67 days with waves in a typical northern hemisphere summer, of which 20 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.