Alibaba Swell Statistics, Autumn: Surf with Light or Offshore Winds
This image shows only the swells directed at Alibaba that coincided with light winds or offshore conditions through a typical northern hemisphere autumn and is based upon 7252 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. Green and yellow represent increasing swell sizes and biggest swells greater than >3m (>10ft) are shown in red. In each graph, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the most common swell direction, shown by the largest spokes, was NW, whereas the the prevailing wind blows from the NE. 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 16% of the time, equivalent to 15 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal northern hemisphere autumn but 5% of the time we expect swell in the range 2-3m (6.5-10ft) 5%, equivalent to (5 days). Taking into account the fraction of these swells that coincided with expected offshore winds, and given the fact that Alibaba is exposed to open water swells, we think that that clean surf can be found at Alibaba about 16% of the time and that surf is spoilt by onshore wind 32% of the time. This is means that we expect 44 days with waves in a typical northern hemisphere autumn, of which 15 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.