Swell Matrix

What Exactly is Wind Swell and Ground Swell?

We all know waves come in different shapes and sizes. The length of the wave, measured in time it takes to pass from trough, to crest, to trough again is called the wave period. Waves less than 10 seconds are considered wind waves or wind swell. Ground Swell is 10 seconds and up, with 20 seconds generally the maximum.

Wind waves, being shorter in length, ‘feel’ the bottom of the ocean less. This makes them peakier and not wrap around points very well.

Long ground swells will usually break all at once at a beach break and close out. Points and reefs are better for ground swell. All the water moving in a ground swell piles up on itself when it breaks and will make the surf height significantly bigger than the open water swell height.

Wind swells are almost always created near to where they are ridden; they lose a lot of energy as they travel from their source. Ground swells can travel halfway across the planet and still provide fun surf.

Surf forecasts often underestimate the size of wind waves- the areas they are created in are often smaller than the size of the grid used in weather models. If you want to score waves to yourself, keep an eye on daily patterns in the observed vs. forecast height. In Southern California, the wind will repeatedly blow overnight off Point Conception and send fun wave for a couple hours to beaches in its wake. Swell Matrix will give you a heads-up when the wind swell is coming but you’ll have to check the buoy or the beach that day for the actual height.

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