This chart illustrates the combination of swells directed at Downtowns over a normal southern hemisphere spring. It is based on 5144 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the coastline so we have chosen the best grid node based on what we know about Downtowns, and at Downtowns the best grid node is 34 km away (21 miles).
The rose diagram shows the distribution of swell directions and swell sizes, while the graph at the bottom shows the same thing without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These occurred only 0% of the time. Green and yellow illustrate increasing swell sizes and red shows largest 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 SW, whereas the the most common wind blows from the S. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Downtowns and out to sea. We group these 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 surfable at Downtowns, you can select a similar diagram that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. During a typical southern hemisphere spring, swells large enough to cause good for surfing waves at Downtowns run for about 93% 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.