This strange pattern at sea is what happens when two wave systems cross each other at nearly perpendicular angles.
Waves can travel thousands of kilometers over the surface of the water.
These are called swells, which is different from ocean waves raised by the local wind.
Another term for wind waves generated and affected by local winds is wind sea.
Then it becomes a swell.
Sea waves and one or more systems of swell waves are frequently present at the same time.
Besides, swells gradually lose energy the further out they travel.
As the swell wave advances, its crest becomes flattened and rounded and its surface smooth.
In such condition a swell might be difficult to perceive.
Finally, a cross sea can only been seen from afar or from the air.
They are not easily visible from the beach.
Here are a few examples that I have managed to find on the web.
Photo credit
Sources:Wikipedia/Weather Online/Komonews
