Arpoador Swell Statistics, May: All Swell – Any Wind
This image illustrates the variation of swells directed at Arpoador through an average May and is based upon 2200 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 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 describes the distribution of swell directions and swell sizes, 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 3% of the time. Green and yellow illustrate increasing swell sizes and largest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how often that size swell was forecast.
The diagram indicates that the prevailing swell direction, shown by the largest spokes, was SSE, whereas the the most common wind blows from the NNE. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Arpoador and away from the coast. We lump these in with the no surf category of the bar chart. To simplify things we don't show these in the rose diagram. Because wind determines whether or not waves are good for surfing at Arpoador, you can load a different image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. In a typical May, swells large enough to cause clean enough to surf waves at Arpoador run for about 55% 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.