Trial Harbour Swell Statistics, Autumn: All Swell – Any Wind
The figure illustrates the variation of swells directed at Trial Harbour through an average southern hemisphere autumn. It is based on 6580 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 Trial Harbour, and at Trial Harbour the best grid node is 16 km away (10 miles).
The rose diagram describes the distribution of swell sizes and swell direction, while the graph at the bottom shows the same thing but lacks 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 illustrate increasing swell sizes and red represents largest swells greater than >3m (>10ft). In either graph, the area of any colour is proportional to how frequently that size swell happens.
The diagram suggests that the prevailing swell direction, shown by the longest spokes, was SW, whereas the the most common wind blows from the WNW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Trial Harbour and away from the coast. We lump these in with the no surf category of the bar chart. To keep it simple we don't show these in the rose diagram. Because wind determines whether or not waves are good for surfing at Trial Harbour, you can select a similar diagram that shows only the swells that were expected 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 Trial Harbour 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.