Rockpiles Swell Statistics, September: Surf with Light or Offshore Winds
This image shows only the swells directed at Rockpiles that coincided with light winds or offshore conditions through a typical September. It is based on 1920 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 the largest swells, greater than >3m (>10ft). In each graph, the area of any colour is proportional to how commonly that size swell occurs.
The diagram implies that the dominant swell direction, shown by the largest spokes, was S, whereas the the most common 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 14% of the time, equivalent to 4 days. Open sea swells exceeding >3m (>10ft) are unlikely to happen in a normal September. Taking into account the proportion of these swells that coincided with forecast offshore winds, and given the fact that Rockpiles is exposed to open water swells, we estimate that clean surf can be found at Rockpiles about 14% of the time and that surf is messed up by onshore wind 33% of the time. This is means that we expect 14 days with waves in a typical September, of which 4 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.