Nahant Beach Swell Statistics, October: All Swell – Any Wind
This picture describes the combination of swells directed at Nahant Beach through a typical October. It is based on 2479 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the shore so we have chosen the optimum grid node based on what we know about Nahant Beach, and at Nahant Beach the best grid node is 35 km away (22 miles).
The rose diagram illustrates the distribution of swell sizes and directions, while the graph at the bottom shows the same thing without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These happened 46% of the time. Green and yellow represent 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 commonly that size swell occurs.
The diagram implies that the most common swell direction, shown by the longest spokes, was E, whereas the the dominant wind blows from the W. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Nahant Beach and out to sea. We combine 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 surfable at Nahant Beach, you can view an alternative image 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 good for surfing waves at Nahant Beach run for about 54% 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.