The figure shows the variation of swells directed at Kogalla over a normal northern hemisphere autumn, based on 5144 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the coastline so we have chosen the most applicable grid node based on what we know about Kogalla, and at Kogalla the best grid node is 35 km away (22 miles).
The rose diagram describes the distribution of swell sizes and directions, while the graph at the bottom shows the same thing but without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These were forecast only 9% of the time. Green and yellow represent increasing swell sizes and biggest 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 occurs.
The diagram implies that the dominant swell direction, shown by the longest spokes, was SSW, whereas the the prevailing wind blows from the W. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Kogalla and offshore. We combine 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 clean enough to surf at Kogalla, you can select a similar diagram that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. During a typical northern hemisphere autumn, swells large enough to cause surfable waves at Kogalla run for about 91% 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.