What does a higher wave period mean?

Long-period waves are also thicker from front to back, so more volume of water is shifted when they break. The combination of those two factors makes longer-period waves more powerful than shorter-period ones .

For boaters, long wave periods (e.g., 12 seconds ) are better for sailing because it typically means most of the waves will be swells which means a smoother ride for small boats.

Average Wave Period is the average period (seconds) of the highest one-third of the wave observed during a 20 minute sampling period . Dominant or peak wave period, DPD, is the period corresponding to the frequency band with the maximum value of spectral density in the nondirectional wave spectrum.

In conclusion: the greater the wave period, 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.