Whoa, Where Did That One Come From?

SwellHow many times have you said that or dreaded it? Well, wave behavior is predictable, but forecasts only tell one part of the story. Remember grading on the curve and the normal distribution? Well, it doesn’t apply to waves. Wave height distributions follow a Rayleigh curve. Which looks like the one below. Click pics for details.

RayleighCurveThat wave forecast is for the significant “H” — the average of the highest 1/3. Beyond that are the highest 1/10, 1/100, 1/1000, etc.

So how big are these larger waves?

HeightDistrA 3-5 foot forecast will include at least some ~6 to ~10 footers!


And if the wave period is predicted to be 6-7 seconds, those larger waves could occur every 1.7 to 1.9 hours… or three could come in a row; remember this is statistical behavior.

This is why the heights and periods found in forecasts need to be more fully understood. And yes, there are 1/10000, 1/100000 and so on waves out there. but conditions usually change before these are seen, unless they don’t, and seen they are.

One response to “Whoa, Where Did That One Come From?

  1. Thank you! I’ve seen “Significant wave height” in a number of forecast tools and never bothered to ask what that meant. E.g. http://forecast.weather.gov/MapClick.php?lat=32.70758&lon=-117.28043&unit=0&lg=english&FcstType=graphical

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