Posties Swell Statistics, Autumn: All Swell – Any Wind
This image describes the combination of swells directed at Posties through an average southern hemisphere autumn. It is based on 5802 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast wind or surf right at the coast so we have chosen the optimum grid node based on what we know about Posties. In the case of Posties, the best grid node is 24 km away (15 miles).
The rose diagram describes 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 were forecast only 0.3% of the time. Green and yellow show increasing swell sizes and red shows highest swells greater than >3m (>10ft). In each graph, the area of any colour is proportional to how often that size swell occurs.
The diagram indicates that the most common swell direction, shown by the longest spokes, was SW (which was the same as the dominant wind direction). Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Posties and out to sea. We group these with the no surf category of the bar chart. To simplify things we don't show these in the rose diagram. Because wind determines whether or not waves are good for surfing at Posties, you can load a different image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. In a typical southern hemisphere autumn, swells large enough to cause clean enough to surf waves at Posties run for about 100% 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.