This chart describes the range of swells directed at 21st Street (Miami) through a typical northern hemisphere summer. It is based on 5080 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 most applicable grid node based on what we know about 21st Street (Miami). In this particular case the best grid node is 26 km away (16 miles).
The rose diagram describes the distribution of swell sizes and swell direction, 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 were forecast 86% of the time. Green and yellow show increasing swell sizes and highest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how frequently that size swell was forecast.
The diagram suggests that the prevailing swell direction, shown by the largest spokes, was NE, whereas the the dominant wind blows from the SE. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from 21st Street (Miami) and offshore. We lump these in with the no surf category of the bar chart. To avoid confusion we don't show these in the rose plot. Because wind determines whether or not waves are surfable at 21st Street (Miami), you can view an alternative image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. Over an average northern hemisphere summer, swells large enough to cause good for surfing waves at 21st Street (Miami) run for about 1.0% 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.