This image shows only the swells directed at Manhattan 26th street that coincided with light winds or offshore conditions through a typical northern hemisphere spring. It is based on 5140 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. Green and yellow represent increasing swell sizes and red shows highest swells greater than >3m (>10ft). 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 longest spokes, was WSW, whereas the the dominant wind blows from the W. 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 20% of the time, equivalent to 18 days. Open sea swells exceeding >3m (>10ft) are unlikely to occur in a normal northern hemisphere spring 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 ratio of these swells that coincided with expected offshore winds we think that that clean surf can be found at Manhattan 26th street about 20% of the time and that surf is spoilt by onshore wind 35% of the time. This is means that we expect 50 days with waves in a typical northern hemisphere spring, of which 18 days should be surfable.
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.