Predicting surf size from swell height.With the advent of our nearshore modelling system we now show a 'nearshore wave height' for a great many locations. This will correspond closely to the exact size of the swell just outside the surfzone and, depending on tides and banks will match closely with the height of the breaking waves on the beach. This model automatically deals with all of the local issues we mention below: What is swell height?
Our wave buoy data and our eight day forecasts both show open ocean swell height. This is the height of the swell as it travels in deep water towards our coasts. This isn't the same thing as the height of the wave on the beach that you're going to surf. Is there a formula or simple bit of maths to convert Swell height to wave height?
No. Sorry. There are some rules of thumb circulating - for instance I've read that if the period is 11 seconds the heights will be the same. Unfortunately there are a number of other factors to take into account and these rules just don't hold up in practice. What other factors influence breaking wave height?
Here is a short, and possibly not complete, list. Bear in mind that I am being incredibly brief here in covering some really complex topics. In time I hope to build more articles to explain further. The main point at the moment is to give you an idea of some of the basics:
It's not all doom and gloom. Clearly there is strong relationship between the swell and the wave! If all other factors are equal its reasonable to assume that todays 20ft@12secs swell will produce a wave something like twice the size of yesterdays 10ft@12secs swell. Many of the factors above (bathymetry as a good example) won't change day to day for your local beach. You won't need to understand exactly how they are working to figure out what makes your favorite break tick. How you approach finding out what does is up to you. You could, if you were really keen, just keep a diary of each session at your local spot, and note the buoy/forecast conditions and the actual conditions. Or a more relaxed approach of just checking the two together will mean that you do get a real feel for what sort of conditions to look for over time. The good news is it is possible to get it pretty much wired for your favorite beach and, while it might take a bit of time and practise, it's possible to really increase the number of good calls and score alot more water time as a result...
Many of these articles are older and some are less relevant now than the used to be. All will be replaced shortly.How it Works
Learning to Forecast
Our Swell Rating
How swell is born
Predicting surf size