Significant Wave Height

The red sky in the morning of two days ago was predicting a period of lots of rain and wind. The natural forecast is never wrong. Today the wind increased to an uncomfortable 30-35 knots with seas building to six meters. Six meters is six meters, but at sea this is a little bit different. The wave height in a forecast is not measured but calculated. I'll spare you the formula but the outcome is called significant wave height. It is the average height (trough to crest) of the one-third highest waves valid for the indicated 12 hour period. Modern technology is using satellites as well; they are able to measure the distance from the satellite to the surface of the sea in centimeters. Thus are also able to measure the wave height as well. On this picture you'll see a significant wave height of 5.6 meter. Normally the air gap under a platform is around twenty meter, preventing the seas (they can reach twenty meters her on this location) from touching the platform.