There are a lot of surf forecast sites out there. Some are free. Some require subscriptions. Some come with fancy color-coded charts. They all say pretty much the same thing based on the same handful of models. Still, if you are relatively new to surfing and you don’t have a degree in meteorology, you might have a difficult time understanding some of the more nuanced aspects of your local surf forecast. The following is a simple guide designed to demystify this information.
What should be the most important and most self-explanatory element of your surf forecast page is actually subject to a long running and heated debate in the surf community. How do we measure wave height? The most accurate answer to that question is: however we feel like it. Six foot in Hawaii is not the same as six foot in California, which is not the same as six foot in Peru and is certainly not the same as six foot in Florida. Some sites measure in feet and other sites use body measurements (waist high, chest high, etc).
What it is: Swell period can be defined as the time between waves. Swell period is typically measured in seconds. So, a swell with a period of 10 seconds would mean that, during sets, waves come every 10 seconds and there are ten seconds between breaking waves. The period for rideable surf is generally between seven and twenty-five seconds.
Why it’s important: Period is just as important, if not more important than surf height. Period is the simplest way to measure a swell’s energy. Put simply, a swell with a large period will have significantly more power than a swell with a shorter period. Many big-wave spots need a swell with a period of sixteen seconds or more to even break. Alternatively, featureless beachbreaks with broad continental shelves are typically better on shorter period swells and close out on long period swells. The most important thing to understand with swell period is that, at many spots, the period will affect the size of the breaking wave. This means that a swell reading 4ft at 18 seconds will be significantly larger than a swell reading 4ft at 8 seconds. Larger periods will also filter into more hard to reach places and rare spots will start to break.
What it is: Surf forecast sites often list swell direction in one of two ways: compass bearings or degrees. In either case, the notation signifies the direction from which the swell is coming, not the direction it is going. So, if you see a SSW swell, this means the swell is coming from the south-southwest. Likewise (for the right-casters), a NE swell is coming from the NE. Degree notation works the same way, but is a bit more exact. Think of a compass as a 360-degree circle.
Why it’s important: Depending on your location, swell direction is either marginally important or extremely important. If you surf a typical east coast beach break with a huge swell window, then swell direction won’t have a huge affect. For example, at an east-facing beach, a north swell will produce more lefts, a south swell will produce more rights, and an east swell will produce either nice a‑frames or closeouts, depending on bottom contour. However, if you are lucky enough to live in an area with an abundance of reefbreaks and pointbreaks, or you live in an area with offshore islands, swell direction is extremely important. Offshore islands may block or distort incoming swells. Reefs and points are generally fixed structures so the shapes of the breaking waves are directly related to a variety of factors, including and especially swell direction.
To best illustrate this, let’s look at some of Southern California’s most iconic waves: Malibu, Rincon, and Lower Trestles. Here we have two rocky points and one rocky reef. These waves are fixed structures with bottoms that don’t move around too much. Rincon is a winter wave that only breaks on swells from a Northerly or Westerly direction. Why? The Channel Islands block south swells from ever reaching the point. For many of the same reasons, Malibu and Trestles are predominantly “summer waves.” Both the Bu and Trestles break best on South swells, and due to island shadowing, they often won’t break at all on a north swell. Malibu is especially interesting because a seemingly insignificant degree shift can alter wave height by several feet. For this reason, it’s important to know which swell directions work beat at different particular breaks, otherwise you may see an overhead swell on the chart, pull up to your favorite beach, and find the ocean completely flat.
What it is: Certain television pundits may not be able to explain why the tide goes in and out, but modern science has pretty much figured it out. The gravitational pull of the moon causes tidal bulges on (high tides) on aligning sides (sublunar and antipodal) of the earth and low tides along the equatorial midpoint of these two extremes. Other factors like the sun and giant landmasses complicate things a bit further, but the pull of the moon pretty much sums it up. Some places have one high tide and one low tide a day (diurnal) and others have two highs and two lows a day (semi-diurnal). Most places follow a 24 hour and 50 minute tide cycle.
Why it’s important: Certain spots are extremely tide sensitive. Some reefs are spectacular at high tide and deadly (or completely exposed) at low tide. Other reefs may be completely underwater at high tide and only break on the low. If your area is prone to large tide swings, or your spot is especially tide sensitive, you need to follow the tide chart to ever really score. Most surf spots also get a small but measurable bump in surf size on an incoming tide.