system
Given the following post, respond as if you're commenting on Reddit:
human
Why do waves come in sets?

I was out diving today in heavy surf and got advice from the dive master to watch for a set of 3 big waves to come by before surfacing - evidently after 3 big ones, you’ll get about 3 or 4 smaller ones, making it much easier to clamber back on to the ladder. I was a little doubtful, but it turned out to provide me the 30 second window I needed to have a substantially easier transition...

But it made me wonder: with the same wind pushing the water, why aren’t all waves approximately the same size? Why do they come in sets of a few waves at a time, instead of hundreds, or instead of randomly variable waves? 

Thanks!
gpt
Wind speeds are variable in space and time and this produces a spectrum of waves of different periods and wavelengths. The longer period waves travel faster in deep water so the waves will sort themselves out as they propagate away from the source. These waves interact and the waves with the shorter periods are modulated by longer period waves producing wave packets that vary in wave amplitude as U experienced diving with small waves followed by larger waves than small waves.  The larger waves occur at the crest of the longer period waves.