Seaford Reef Swell Statistics, Autumn: All Swell – Any Wind
This chart describes the variation of swells directed at Seaford Reef through a typical southern hemisphere autumn and is based upon 5140 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the best grid node based on what we know about Seaford Reef. In this particular case the best grid node is 55 km away (34 miles).
The rose diagram shows the distribution of swell sizes and directions, while the graph at the bottom shows the same thing without direction information. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These happened only 91% of the time. Green and yellow represent 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 commonly that size swell happens.
The diagram implies that the prevailing swell direction, shown by the longest spokes, was SW, whereas the the dominant wind blows from the SSE. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Seaford Reef and away from the coast. We group these with the no surf category of the bar chart. To keep it simple we don't show these in the rose plot. Because wind determines whether or not waves are clean enough to surf at Seaford Reef, you can select a similar diagram that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. Over an average southern hemisphere autumn, swells large enough to cause surfable waves at Seaford Reef run for about 3% of the time.
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.