Swell: waves travel in train carriages

The swell period is one of the most underestimated surf forecasting variables checked by surfers. The quality of the waves largely depend on the time between sets.

The amount of time it takes for two successive wave crests to pass through a determined point is called swell period or wave interval.

The swell period is a critical variable in surf forecasting because it will ultimately measure the quality of the upcoming surf session.

Interpreting the interval between wave sets is, therefore, relevant to surfers and surfing. High quality waves - ground swell - are generated in open ocean, hundreds of miles offshore. Do you usually check wave period forecasts for your region?

Short intervals of time - between 1 and 10 seconds - may indicate that one spot is pumping surf generated by local winds or regional wave currents. This means low quality surf.

When surf report data tells us that we might be getting a 20-second period between waves, as well as light offshore winds, the chances of enjoying a glassy, perfect-peeling wave experience will dramatically increase.

The National Oceanic and Atmospheric Administration (NOAA) notes that the peak period identifies either the period (the time between waves) associated with the locally generated wind sea (in cases with strong local winds) or the dominant wave system (swell) that is generated elsewhere.

Long-period swells accumulate energy, travel faster, and can easily cope with local winds and currents, resulting in larger surf, when it comes to average wave height.

Forerunners are the first waves coming in the long-period swells. They usually move faster that the remaining carriages of the wave train.

Although forerunner waves carry a large amount of energy, they are not easily spotted by surfers because they don't show much surfing potential. What they do indicate is that more quality waves are coming in on the horizon.

Conclusion: the greater the wave period is the better the swell. Also, take a look at how waves are formed, the difference between ground swells and wind swells, and the effects of shoaling and refraction in wave height.

The Wave Period Table of Quality Surfing:

Wave Period (s) Wave Conditions
1-5 Local wind swells with bumpy and disordered waves. Poor surfing conditions;
6-8 Regional and local wind swells with average surfing conditions. Offshore winds might get it better;
8-10 Medium-distance swells improve the local surfing conditions. Go for it;
10-12 The power of ground swells is taking effect; Definitely worth it;
+13  A long period swell brings high-quality waves. Epic surf session ahead;