Swell-Forecast.com - European SURF forecasting

Directional spectra.

The directional spectra predictions are probably best appreciated by the user who has some basic oceanographic or meteorological knowledge. They are combined plots of wave energy (which relates to height), wave frequency (the inverse of period) and direction, at a single point on the surface of the ocean.

The directional spectra plots are available for the same locations as some of the wavebuoys around the UK. However, the data does not come from the buoy, instead it is generated from a mathematical model, and is a prediction, not an observation.

The usefulness of these charts is to show the expected development of swell in energy level, direction, and frequency over the coming days. For example, a long period southwest swell might arrive followed by a northwest windsea. More information is available at a glance than the wave height contour maps, but the disadvantage is that the prediction is only for a single location.

The wave energy level is represented by different colour contours, the direction of each particular energy level is whereabouts that contour is around the circle, and the frequency is radial distance from the centre of the circle. Concentric circles are at intervals of 0.025Hz starting with 0.025Hz in the middle. Therefore the second concentric circle would be 0.05Hz (= 20s period). An estimate of the significant wave height is also shown with each plot, together with a wind arrow.

The example below shows a swell with energy levels corresponding to a significant wave height of 2.38m. The peak of the spectrum is at about 15s, and the swell is coming from the northwest. The wind is from the west.