Wellington Region Emergency Management Office says:
Swell Warnings explained! 🌊 For those of you who have seen the swell warnings come out and are wanted to know a bit more about how these work - take a look at this great explainer video put together by @MetService.
Essentially: waves come in all different heights. To get “significant swell height” they look at the size of the largest one third of all waves over a point. They measure the waves from bottom to top (trough to peak). Then they average that height.
Significant Wave Height is the average of the height of 1/3 of all the waves. The height of the tallest wave gives the Maximum Wave Height. There can be as much as 50% difference between Significant and Maximum Wave Height.
