The Wave Period, which is reported by every major surf condition reporting web site, tells the time it takes for two wave peaks to pass by. Essentially it’s telling how far apart the waves are, but it’s measured in the time it takes for two to go by rather than the true distance between.
So why is this important? The wave period, rather than the wave size, really defines the quality of the wave. The longer the period, the faster the wave is moving. The faster the wave is moving, the more powerful the wave is and the “deeper” the wave is beneath the surface of the water. As “deep” waves approach land, they are pushed up, making a larger wave.
So for example, a wave that is 2 feet tall and a 4 second period will likely have about a 2 foot face when it hits shore. But give a 2 foot wave a 10 or 12 second period and it will likely have more like a 4 foot face when it hits the shore.
The wave period is also a rough measure of how far the wave has travelled. If you look at your local wave buoy on a windy day you’ll likely see what the “normal” wave period for wind waves created by local winds is. To look for good waves to surf, you’ll want to look for waves with a longer period than the “normal” waves. This indicates that the waves are likely to be coming from a more powerful storm further away.
So, a good rule of thumb is that it’s more important to look at wave period than wave height to see if there is some surfable swell coming through.