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 over a normal September and is based upon 2400 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 show increasing swell sizes and red represents the highest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how commonly that size swell was forecast.
The diagram implies that the prevailing swell direction, shown by the largest spokes, was S, whereas the the dominant 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 19% of the time, equivalent to 6 days. Open sea swells exceeding >3m (>10ft) are unlikely to occur in a normal September but 7% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 7%, equivalent to (2 days). Taking into account the proportion of these swells that coincided with predicted offshore winds, and given the fact that Rockpiles is exposed to open water swells, we calculate that clean surf can be found at Rockpiles about 19% of the time and that surf is blown out by onshore wind 33% of the time. This is means that we expect 16 days with waves in a typical September, of which 6 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.