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 2302 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 red shows biggest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the most common swell direction, shown by the biggest spokes, was S, 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 20% of the time, equivalent to 6 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise 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 expected 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 20% of the time and that surf is messed up by onshore wind 32% of the time. This is means that we expect 16 days with waves in a typical September, of which 6 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.