Back to Surfbreak Theory
Intelligence·9 min read
Reading Long-Period Swell
Period — measured in seconds between wave crests — tells you more about a coming swell than height ever will.
A 4-foot, 17-second swell will overpower a 6-foot, 9-second swell at almost every reef on Earth. Period reflects energy, and energy is what bends around headlands, refracts onto reefs, and produces the open faces we paddle out for.
Anything 14 seconds or above is groundswell. Below 10 seconds is windswell — local, choppy, short-lived. The sweet spot for most reefs is 13–18 seconds.
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