Groundswell vs Wind Swell
Wind waves are generated by local wind and are still being driven by it — short-period, steep and disorganised. Groundswell has left its generating storm behind and travelled, sorting itself into long-period, orderly sets.
Almost every sea state is a mixture. The useful skill is not classifying a day as one or the other but reading how much of each is present.
How they form
Wind transfers energy to water through friction and pressure differences. Close to the storm, the result is a chaotic sea of many periods at once — wind waves. As that energy propagates away, dispersion sorts it: longer-period components travel faster and pull ahead, arriving first and cleanly separated. That sorted, travelled energy is groundswell.
Distance is what does the work. A storm 3,000 miles away delivers beautifully organised long-period lines. The same storm overhead delivers a mess.
Telling them apart on a report
Compare dominant period against average period. When DPD and APD are close, the sea is dominated by one train. When DPD is much longer than APD, there is a groundswell underneath with wind chop layered on top — a common and often good combination, provided the local wind is not also ruining the surface.
Stations with spectral sensors report the components separately, which removes the guesswork entirely.
Why it matters for where you surf
Exposed coasts pick up groundswell readily and can be overwhelmed by it. Sheltered and island-shadowed spots may need it, because short-period wind swell lacks the reach to bend into them at all. Break-specific behaviour is covered in each spot's swell-window guide.
See it on live data
The fastest way to make any of this concrete is to go and look at the numbers being described.
Common questions
Is groundswell always better?▾
How far does groundswell travel?▾
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