Avalanche Swell Statistics, Autumn: Surf with Light or Offshore Winds
This image shows only the swells directed at Avalanche that coincided with light winds or offshore conditions over a normal northern hemisphere autumn and is based upon 7252 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 biggest swells greater than >3m (>10ft) are shown in red. 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 biggest spokes, was NNW, whereas the the prevailing wind blows from the ENE. 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 42% of the time, equivalent to 38 days. Open water swells exceeding >3m (>10ft) only occur 1.2% of the time in a typical northern hemisphere autumn, equivalent to just one day but 14% of the time we expect swell in the range 2-3m (6.5-10ft) 14%, equivalent to (13 days). Taking into account the proportion of these swells that coincided with expected offshore winds, and given the fact that Avalanche is exposed to open water swells, we calculate that clean surf can be found at Avalanche about 42% of the time and that surf is messed up by onshore wind 20% of the time. This is means that we expect 56 days with waves in a typical northern hemisphere autumn, of which 38 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.