Asu Swell Statistics, Winter: Surf with Light or Offshore Winds
This image shows only the swells directed at Asu that coincided with light winds or offshore conditions through a typical northern hemisphere winter and is based upon 6931 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 show 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 frequently that size swell was forecast.
The diagram suggests that the dominant swell direction, shown by the longest spokes, was SSW, whereas the the dominant wind blows from the W. 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 64% of the time, equivalent to 58 days. Open sea swells exceeding >3m (>10ft) are unlikely to occur in a normal northern hemisphere winter but 27% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 27%, equivalent to (25 days). Taking into account the proportion of these swells that coincided with forecast offshore winds, and given the fact that Asu is exposed to open water swells, we estimate that clean surf can be found at Asu about 64% of the time and that surf is messed up by onshore wind 36% of the time. This is means that we expect 91 days with waves in a typical northern hemisphere winter, of which 58 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.