How To Forecast The Surf – Lesson One: Swell Profile

Guess what, it’s easy to forecast the surf. It doesn’t require a degree in oceanography or any kind of psychic ability. All it takes is a little diligence and an internet connection. When coupled with personal observations and experiences, you’ll eventually discover your own preferred conditions, which may be used to tune and improve your surf forecasting skills.

To help you become a better surf forecaster, we will be posting a series of lessons on how to use Buoy Alarm to predict ocean conditions. In this, the first lesson of the series, we’ll explain how to use our buoy forecast charts to determine a swell profile.

Lesson One: Swell Profile

A variety of factors can influence surf quality, including wind, weather, and tidal conditions. However, none of those variables matter if there is no swell in the water. The first step to crafting a surf forecast involves knowing when waves will arrive.

Wait a minute, you may be asking, isn’t that exactly what a surf forecast is? Knowing when waves will arrive? Well, yes, but it’s also the easiest part. There’s a big difference between knowing when surf will arrive, and knowing when good surf will arrive. Let’s continue…

Ocean waves are generated by surface winds and may travel thousands of miles before making landfall. The size and quality of a swell is the direct result of the speed, duration, and direction of the surface winds that produce it. Because of this, many surf forecasters analyze wind and pressure data to identify and track wave-producing storm systems. Long-term forecasts (greater than 7-days ahead) depend on the interpretation of this wind and pressure data, but accurate near-term forecasts (3-5 days away) can be achieved using Wavewatch III model data.

The chart above displays the 102-hour (January 11, 2011 at 2:00 p.m. HST) Wavewatch III wave height forecast for the Pacific Ocean. This chart provides a broad overview of the Pacific, showcasing individual storm systems in both the Northern and Southern hemisphere, and is arguably the easiest method of identifying a swell. Anything above a teal blue represents a wave height of 10-feet (the chart is in meters), so if you’re seeing reds and purples, it’s really, really big.

While it is easy to determine the rough size and arrival time of a swell using this chart, it does not provide swell component data. Also, each image is 6 hours apart, which makes it difficult to determine when a swell will reach its peak. Let’s zoom into the Hawaii region and take a closer look at the Eastern North Pacific model:

Zooming into the region reveals several bands of increasing wave height, but the resolution of the chart is still pretty low. We can see wave bands bending around the islands, but no swell details are available.

Let’s take a look at the same timeframe on the Waimea Bay buoy forecast, which is also being generated by the Wavewatch III model:

Applying the Wavewatch III model to a single point as opposed to a broad region produces much more data, including detailed wave height, period, and direction for each of the swell components in the water.

In fact, detailed swell information for any hour within the seven-day forecast window may be shown by mousing over the chart. You may also click and drag to select a particular time-frame, and the chart will zoom into your selection. Let’s zoom into Tuesday for a closer look:

We can see that the swell will already be quite sizable by first light, having built overnight. The swell peaks Tuesday afternoon at 4:00 p.m. (14.1 feet at 14.0 seconds 315°), then slowly declines through Wednesday. Aside from the primary Northwest component, there is also a small, short-period West swell in the water. This component is unlikely to cause any combo-swell conditions, given it’s small height and short period.

The general profile of the swell can be summarized as such: builds Monday night, peaks Tuesday afternoon, slowly declines into Wednesday. Given this information, we can begin to take a look at other influential factors, such as wind, which is what we’ll be discussing in the second lesson.

In the meantime, check our buoy location map to find a forecast in your area. Here are a few we suggest looking into:

Northern California: Half Moon Bay, 357 NM West of San Francisco

Southern California: Harvest, Point Loma South

Florida: 120 NM East of Cape Canaveral

New York: 23 NM Southwest of Montauk Point

Additional Resources: Wind Waves on Wikipedia, The NOAA Wavewatch III Model