The rose diagram illustrates the combination of swells directed at Areia Preta through a typical October and is based upon 1736 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 most applicable grid node based on what we know about Areia Preta, and at Areia Preta the best grid node is 32 km away (20 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 show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These were forecast only 38% 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 occurs.
The diagram indicates that the prevailing swell direction, shown by the biggest spokes, was ENE, whereas the the most common wind blows from the ESE. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Areia Preta 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 plot. Because wind determines whether or not waves are clean enough to surf at Areia Preta, you can select a similar diagram that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. Over an average October, swells large enough to cause surfable waves at Areia Preta run for about 62% 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.