Reading Surf Forecasts: What Can Go Wrong
In the last article we went over the 7 most common metrics you’ll see on a surf forecast. In this article we’ll talk about the ways a good looking 4–5 foot swell can go wrong and how you can use the metrics besides swell height to figure that out.
Wrong Direction — Check out La Jolla Shores — if there’s a swell coming from directly south the shores will most likely see little to none of it because the Village of La Jolla blocks swell from that direction.
Wrong Period — Period describes the time between waves but that’s not why surfers care about it. We care because it’s directly related to wave power and wave diffraction. Why we care about wave power is obvious and a longer period swell will have more power.
In order to understand wave diffraction we must realize that waves bend around corners. If you are standing on the south side of a square building and your friend yells for you from the west side of the building you can hear her but you can’t see her — this is because sound waves are bending around the southwest corner of the building.
Ocean waves do exactly the same thing. The important idea here though is not just that they bend but that the amount of energy they keep while bending is related to the wave period. Longer period waves will keep more energy as they bend around corners.
That means that if there’s a long period swell coming from the southwest without a direct path to La Jolla Shores (because it’s blocked by La Jolla Village) we still may see good sized waves at La Jolla Shores — the waves will keep more power as they diffract around La Jolla Village.
Wrong Wind Direction/Speed — Wind can have a significant impact on waves — the same exact swell can be turned from an epic, barreling tube into a sloppy pile of junk by a change of the wind.
Our 4–5 foot swell would be best served by no wind or a slight offshore wind. No wind would keep the waves pristine and a slight offshore (towards the face of the wave) would help to hold the waves vertical longer. A vertical wave is desirable because it allows you to generate speed easier.
Wrong Tide Height — Tide height matters because the ocean floor matters. The ocean floor is the wave — it is directly responsible for the shape of the wave.
The 4–5 foot swell we have our eyes on might peak during a very low tide. If we’d like to surf a spot that becomes very shallow during a low tide then we’re going to be surfing in a spot without much water between us and the bottom. This might be ok if we’re particularly skilled or if the bottom is sand but otherwise it’s probably best to surf at a different spot or a different time.
Similarly we might want to surf when the tide height is quite high — in this case we might have the opposite problem and there may be too much water between us and the features of the ocean floor that create good waves. You’ll hear surfers talk about how a spot is “mushy” or “slow” — these can be indicators that the tide is too high for the spot.
To be clear, not all breaks follow the above example — some work well when its a very low tide, a very high tide, or even both.
Each surfing spot has one or more sets of ideal conditions — it’ll work best on a 3 foot, 15 second swell if it’s from 200° and the tide is around 5 feet but it’ll also work on a 6 foot swell if it’s from 270° and the tide is between 0 and 3 feet. To find these ideal conditions you’ll need to either surf the spot regularly and keep track of what conditions work (plenty of apps exist to help you do this) or you’ll have to talk a salty old timer into telling you when it’s best.
Getting to know how to read a surf forecast and understanding how the metrics translate into waves is a vital step to becoming a competent surfer — stay tuned for more deep dives into the metrics and how they are collected.
In our next post, we’ll go into detail on the metric that most people pay exclusive attention to – swell height.
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