How to measure wave height in surfing

Surfers have always had different ways of measuring waves. What is wave height? How should a wave be measured?

Surfing is a sport of achievement. The first wave ride, the first surf line, the first barrel, the biggest wave…all stories to tell and bars to be raised. One of the most famous surfing quotes speaks volumes about surfers and their passion. “You should’ve been here yesterday,” it goes.

Buzzy Trent, a big wave surfer, once said that “…waves are not measured in feet and inches, but in increments of fear”. A statement like this raises questions. Chiefly, how can we standardize the measurement of waves in order to make accurate comparisons?

There are two main approaches to measuring wave height.

The Bascom Method and the Hawaiian Scale

The Bascom Method, developed by Willard Newell Bascom, is widely regarded as simple, fair, and rational; yet an overestimation most of the time.

One stands on the beach with eyes aligned with wave crest and the horizon. He or she then measures the wave from that point to the average sea level. Californians loved it.

The Hawaiians saw things differently. They were known for measuring their waves from the back, effectively cutting the determined height of the waves they had ridden in half. The method used by the Californians, they thought, was full of exaggerated bravado.

When big wave surfing got the attention of the media, the Hawaiian Wave Scale conquered fans. It was really cool to underestimate the size of a wave.

The Hawaiian Wave Scale has a few disadvantages.

It is difficult when measuring small waves; can’t be confirmed from the beach; is based on emotional variables like courage; it does not measure the entire face in which surfers ride, and it doesn’t apply to waves that are big and heavy, but lack a large backside, like Teahupoo.

The Surfable Wave Face Method

There is a third way. This fair and balanced approach is based on the area that is actually ridden by a surfer.

Keeping in mind that the bottom-turn is the lowest point on the wave face, the Surfable Wave Face hypothesis would consider 2/3 of the Bascom Method as the area where surfers draw their lines and tricks, from the pocket almost to sea level.

In conclusion: a 6.5 feet wave measured with the Bascom Method would correspond to a 3.2-foot wave on the Hawaiian Scale, and 4.2 feet using the Surfable Wave Face measurement system.

So it seems that the logical application of the Surfable Wave Face method brings the best of the “underestimated” and “overestimated” models into a balanced, globally accepted system of wave measurement for competitive surfing.

How To Read The Buoys

Most of the buoys in the United States are run by the National Oceanic and Atmospheric Administration’s (NOAA) National Data Buoy Center. Individual buoys can be accessed on the internet via NOAA’s website. Here’s how to read them:

Wind

Wind, and more precisely, where it’s coming from and how fast, is the second most important surf-affecting variable other than wave size. It’s also constantly changing and difficult to predict with much precision. Because onshore wind (blows from the ocean towards land) is detrimental to surf conditions, and conversely, offshore wind (blows from land out to sea) is optimum, it’s a good idea to understand how to get up-to-date wind information from your local buoy.

The two variables that influence wind conditions are wind direction and wind speed, and both are important. Wind direction tells you the direction the wind is blowing from. Wind speed is the speed the wind is blowing, measured in knots. For example, if the buoy’s wind reading says the direction is NNW at 15 kts with 25 kts gusts, that means the wind is blowing out of the north/northwest, at 15 knots, with occasional gusts of up to 25 knots. For surfing, that’s a lot of wind, but if you have access to a break that faces south, the wind will funnel straight offshore.

Waves

This one takes the top honor in terms of importance to the surfer. If there are no waves, it really doesn’t matter what the wind direction is or how high the tide is – you’re not surfing anyway. And while all the surf-forecasting websites do a pretty decent job of giving you accurate swell information, any individual swell event goes through a lifespan that ranges from building, to peaking, to dying out, and eventually fading completely. Check in with your local buoy to see exactly what the swell is doing at that exact hour.

There are two variables that contribute to the size of a wave when it breaks: wave height and wave period. What? There’s more to waves than their height? Oh, you have so much to learn.

The period describes time elapsed between individual waves within a given wave set. For example, a period of 14 seconds means that when a set of waves reaches the beach, about 14 seconds will elapse in between each wave that breaks. Interestingly, a wave’s period is extremely significant because it directly affects both size and power. Period translates into the distance between two waves as well as the depth, meaning the longer, or deeper, a wave’s period, the bigger and more powerful it will be once it reaches its breaking point. Therefore, a wave with a long period will actually have more deep-water energy than a wave with a short period, giving it more height and power when it breaks.

A buoy’s wave height reading is exactly what it sounds like: the height, given in feet, from the peak of each wave to its trough. Keep in mind that buoys will automatically average out both the wave height and wave period.

So how do you determine actual wave height from both size and period? To know how a certain swell will affect your local surf conditions, you need to understand how particular breaks respond to both short period swell (also called wind swell) and long period swell. You also need to quantify the height and period into a single overall estimation of wave height. While experience is the only way to get really good at determining this somewhat elusive value, you’ll quickly learn that a swell reading six feet at 18 seconds is a lot bigger than one registering 10 feet at eight seconds.

Temperature

In addition to wind and wave height, buoys also compute both air and water temperature.

Other Factors: Tide & Swell Direction

Tide and swell direction are secondary factors when determining surf quality, although both are extremely important. Blissful ignorance to tide and directions will only be blissful for so long.

Swell direction is an obvious factor when deciding when and where to surf. If a moderate-sized swell is rolling in from the south, you shouldn’t head to a beach that faces north unless you want to do more fishing than surfing. On larger swells, it’s sometimes wise to check spots that aren’t openly facing the brunt of the swell in order to access friendlier waves.

Ever wonder why surf shops give out those little tide books at the front counter? Every surfer should be aware of the day’s tidal scenario when deciding when and where to surf. Most surf spots have a particular tide that works best with that spot, and outgoing and incoming tides can affect rip currents and wave consistency. While some breaks may function on any tide, many more will altogether shut down if the tide is too low or too high. Getting to know your local surf spots and what tides they prefer is an important step towards getting quality surf as often as possible.

Quantum Physics and Surf Forecasting

At the moment the wave charts are not looking too epic. However, in about a week’s time things are due to improve as the general situation over the North Pacific  changes.

“That’s all I can say. Why? Because the best way to look at the long-term charts is to just get a general picture and not try to be too specific; otherwise you’ll be frustrated when the forecast keeps changing.”

Forecasting is a trade-off between three parameters: precision, accuracy and length. If we want a really detailed forecast it needs to be short-term; otherwise it won’t be accurate. Likewise, if we want an accurate long-term forecast we mustn’t specify too many details.

As our understanding of the atmosphere and ocean improves, and computing power increases, forecasts will, of course, get better. But there are several reasons why they will never be perfect: the most fundamental of which has to do with their dependence on initial conditions.

Atmospheric and oceanic prediction models rely on initial measured values of parameters such as pressure, windspeed and temperature. The more accurate these measurements are, the better the prediction will be.

The ocean-atmosphere system is highly complex and behaves in a non-linear way, with feedback loops, tipping points and snowball effects. Any slight errors in the initial measurements will not only feed through to the end result, but will be amplified. As the forecast length increases, so does the amplification of errors, so that the forecasts end up diverging uncontrollably.

So, all we need to do to get that perfect forecast is to measure those initial conditions perfectly. In fact, this is what the great French physicist Pierre-Simon Laplace (1749-1827) had in mind. He postulated that, if we could somehow measure the exact position and velocity of every particle in a system, we could use Newton’s laws of motion to predict their next position and velocity, and the next, and so on. As long as we knew the present, we could predict the future

Laplace’s hypothesis – called determinism – was proved wrong about a century later. Scientists like Werner Heisenberg (1901-1976) started discovering the paradoxes of quantum mechanics, one of which is that you cannot measure the position and velocity of a particle at the same time.

This means you can never describe the present state of anything with 100 per cent accuracy. And if you can’t describe the present state with total accuracy, you’ll never be able to make an error-free prediction of the future.

So, bearing in mind that there are inevitably going to be errors, the best thing we can do is to know how precise to be, and when. The MSW ‘probability’ parameter helps us do that by giving us an idea of how confident we can be of a particular forecast. You’ll notice that it doesn’t just change with forecast length – but I’ll talk more about that in a future article.