Off Donegal they measured a wave at 67’ (20.4m), the highest wave recorded in Ireland. The Irish Met Office says the buoy that measured it is 11km off the coast, so it was generated in deep water by the persistently high winds.
I was once in very large waves, around 45 feet, off the east coast of the USA and there was a point at which I didn’t think the boat was going to make it up the face of a particularly steep wave. An illusion, of course, but pretty scary nonetheless.
The probable maximum height of wind waves is around 80% of the wind speed. So, a 50 knot wind blowing over an area of ocean with unlimited fetch would produce a maximum wave height of about 40 feet. This height is achieved after it has been blowing for a day, having doubled in height since the first four or five hours of the storm. Further maximum wave height increase is more subdued, it takes two days to get that wave up to 50 feet in height.
The average wave height in a storm is about half the height of the top ten percent of waves and one third of the highest wave. So, if the maximum wave height in our 50 knot blow is 40 feet, the top ten percent of waves will be about 20 feet and the overall average will be about 14 feet. It doesn’t sound so bad when you put it like that, does it? Except that you still have to survive those pesky maximums and top ten-percenters!
