This image shows only the swells directed at Manhattan 26th street that coincided with light winds or offshore conditions through a typical northern hemisphere autumn. It is based on 5144 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. Green and yellow illustrate increasing swell sizes and red illustrates the biggest swells, greater than >3m (>10ft). In either graph, the area of any colour is proportional to how frequently that size swell happens.
The diagram suggests that the dominant swell direction, shown by the largest spokes, was WSW, whereas the the prevailing wind blows from the WNW. The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 35% of the time, equivalent to 32 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal northern hemisphere autumn but 5% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 5%, equivalent to (5 days). Taking into account the proportion of these swells that coincided with forecast offshore winds we think that that clean surf can be found at Manhattan 26th street about 35% of the time and that surf is messed up by onshore wind 26% of the time. This is means that we expect 56 days with waves in a typical northern hemisphere autumn, of which 32 days should be clean enough to surf.
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.