Waves Explained

To talk about waves and surf we need a bit of basic terminology. Even something as simple as ‘wave height’ has different meanings and interpretations – by understanding the ‘common language’ of surf forecasting you’ll have a much better idea of the pitfalls of interpreting your model forecast.

Maximum Wave Height

Magicseaweed delivers some very precise information about expected swell heights at your local beach for the next ten days. However anyone who’s ever been surfing will know that even on the perfect day not every wave that comes through the line up will be the same size. We go into some detail here about this but to summarise the heights we (and every other surf forecaster around) give are ‘significant height’ which is the average of the largest third of waves. It’s close to saying the same as ‘the average height of the set waves’. Fortunately there’s a fairly good relationship between this number and the height of the largest […]

Waves Explained – A Hypothetical Example

In a perfect world a wave looks very simple. The height of a wave is the total distance from it’s peak to it’s trough. The period is the time, in seconds, that it takes for a first then second wave to pass the same point. In other words the time in seconds between successive peaks or troughs. Interestingly for us as surfers this number is consistently related to both a swells speed and the depth of water in which it can start to react with the seabed. This makes it something of a magic number for determining how a swell will transform itself into surf at your beach (something we’ll […]

Waves Explained – A Real World Example

In the real world we don’t have perfect waves, of equal height and period heading in the same direction at the same time. Standing on the cliffs above the beach you can see this for yourself. The ocean varies from day to day, sometimes a regular consistent line of waves will approach the beach, on other occasions the ocean may appear a confused jumble of waves heading in slightly different directions and of different sizes. The state of the sea is always more complex than groups of identical waves, especially nearer to the storms that create them, and so although we often describe the state of the sea as though […]

Measuring Wave Height

As surf forecasters we measure waves from the trough (the lowest point) to the peak (the highest point). Typically we do this in feet but of course it’s equally valid in meters. Surfers however indulge in a range of different measuring systems depending on their context which all usually involve underestimating the face height of the waves. The ‘Hawaiian’ system is intended to measure not the breaking wave face, but the height of the back of the wave as viewed from the water. In doing this the measured height of waves breaking on reef (which tend to pull a deeper trough in front than our ‘idealised’ image of a normal […]