A Guide To The New Kid On The Surf-Forecasting Block
“When you’re glancing at estimated wave heights, wave energy will help you get an idea of how punchy those waves will be — in the same way that volume tells you how much foam a board will contain.”
That was a quote from stabmag.com in a piece titled “Why The Fuck Are We Measuring Waves In Kilojoules?” Wave energy is increasingly being used in surf forecasting and can help surfers score better waves or find conditions better suited to their skill set.
If you are of a certain age, you may remember when surfboards weren’t measured in volume. It was a different era; dinosaurs roamed the earth, a selfie was a very private thing, music was played on shiny silver discs, and surfboards came with just three identifiers: length, width, and thickness.
That changed in the early 2000s. Surfboards started to be made with computer-aided design (CAD) technology, which allowed volume to be calculated with the press of a button. It was a helpful tool. Two surfboards with the exact dimensions (let’s say a 6’3” x 2 1/2” x 19” wide) could be very different beasts. That was because the board’s width and thickness are only measured at the widest and thickest point of the surfboards, and so doesn’t give the complete picture of the board’s shape.
The volume did, to the nearest milliliter, and two decades later, it has become the defining metric of a surfboard. Well, except for my 50-year-old Aussie mate Maddo who, like the Japanese soldier who continued fighting alone for 30 years after the end of WW2, refuses to have anything to do with, in his words, “all this liter bullshit”.
In surf forecasting, we are going through a similar revolution. Most surf forecasts have always provided us with a swell measurement based on the gold standards of wave heights and swell period and then factored in swell and wind direction.
Surfers knew that a more extended period meant more powerful swell and bigger waves. But working out the size of a 4ft at 16-second period swell versus a 6ft at 14 seconds was impossible.
Till now, wave energy in scientific terms is the measurement of energy per meter cubed in a wavefront. It is determined by combining the effect of all swell heights and their periods at a single offshore location and at a point in time. By factoring in swell direction and local bathymetry, you can measure the offshore energy that arrives at your spot. That tells you how powerful the waves are going to be. It factors in that while an 8ft swell may produce solid, hollow waves at an exposed reef, the beach around the headland with a gentle sand profile will offer crumbling, longboarding waves. It’s the same swell, but you know which one you’d rather be caught inside by.
Surf-Forecast (https://www.surf-forecast.com) is a site that has pioneered the energy rating system, using a single number measured in kilojoules for each report and forecast at every location worldwide. For more than five years, many of its millions of users have come to rely on this simple metric as much as the height and period.
“It’s all about those sweet, sweet kilojoules,” was one comment on a Reddit thread I found discussing wave energy. “I live in Indo, and one of my favorite waves only works with less than 350 energy, so I’m the opposite; always hoping it will drop below that,” was another.
With the energy rating giving you a snapshot of the power of the ocean and whether it’s trending up or down, surfers can work out whether the waves will be in their comfort zone.
Surf-Forecast advises that wave energy of 100kJ can be just about surfable at many breaks, and 200-1000kJ should produce increasingly punchy waves. At the same time, 1000-5,000+ can start to get really heavy and even dangerous at some breaks. As a reference, the last day of the Pipeline Pro came in at around 1800kJ.
Surfline has also recently added a metric for its premium users in the new Swell Spectra tool. “Surfline is trying to educate newer surfers about the idea that not all 5-foot waves are equal,” said Surfline’s Data Scientist Daniel Thompson in the Stab article. “A swell of 5 feet at 10 seconds makes a 5-foot wave, and a swell of 2.5 feet at 20 seconds also makes a 5-foot wave. The energy, though, will be very different.”
With surf forecasting, the fundamentals of swell size and period will remain the most important aspects of predicting the conditions at your local or on your next trip. That can help you decide what board to ride on your next surf or what quiver to bring on a strike mission overseas. Wave energy rating is now a vital new tool, and we’d advise you to add it to your surf forecasting kit.