Arpoador Swell Statistics, Autumn: All Swell – Any Wind
The figure describes the range of swells directed at Arpoador over a normal southern hemisphere autumn, based on 6580 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the best grid node based on what we know about Arpoador. In the case of Arpoador, the best grid node is 21 km away (13 miles).
The rose diagram shows the distribution of swell sizes and swell direction, 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 occurred only 1.8% of the time. Green and yellow illustrate increasing swell sizes and red illustrates highest swells greater than >3m (>10ft). In either graph, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the prevailing swell direction, shown by the largest spokes, was SSE, whereas the the dominant wind blows from the NE. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Arpoador and offshore. 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 good for surfing at Arpoador, 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 southern hemisphere autumn, swells large enough to cause clean enough to surf waves at Arpoador run for about 44% 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.