Ammonias Swell Statistics, Autumn: All Swell – Any Wind
The rose diagram describes the combination of swells directed at Ammonias through an average northern hemisphere autumn. It is based on 7252 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the most applicable grid node based on what we know about Ammonias. In the case of Ammonias, the best grid node is 37 km away (23 miles).
The rose diagram shows the distribution of swell sizes and swell direction, while the graph at the bottom shows the same thing but lacks 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 92% of the time. Green and yellow illustrate increasing swell sizes and highest swells greater than >3m (>10ft) are shown in red. In either graph, the area of any colour is proportional to how frequently that size swell occurs.
The diagram suggests that the prevailing swell direction, shown by the biggest spokes, was S, whereas the the dominant wind blows from the ENE. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Ammonias 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 plot. Because wind determines whether or not waves are clean enough to surf at Ammonias, you can view an alternative image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. In a typical northern hemisphere autumn, swells large enough to cause surfable waves at Ammonias run for about 8% 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.