Swell chart: the red fetch is coming to your surf spot

Surf reports are a result of swell and wind chart analysis. Tracking the direction, strength, and duration of incoming waves and winds are key components for surf forecasters.

The best swell conditions for great surfing sessions can be spotted by everyone.

You don't need to be a professional weather forecaster in order to understand how, when, and where the best spot is for surfing waves.

Waves are a result of the energy applied by winds on the surface of seawater. The large areas affected by the winds on the oceans are called fetch, and fetch is in constant mutation.

When we look at a swell chart, we see circular colored fetch with corresponding significant wave height.

The edges of the fetch will usually reach our shores in a matter of hours or days. But can we calculate exactly when the ground swell will reach the shoreline?

Swell Math

It's quite easy. There's a simple math equation.

Knowing that a swell will travel, on average, at 1.5 times its period in nautical miles per hour, we only need to check the average wave period and the distance of the fetch.

So, if there's a good-looking fetch at 2,500 nautical miles heading to our surf spot, with an average period of 15 seconds, the calculation is as follows:

  • 2,500 nautical miles x (15 seconds of wave period x 1.5) = 111.1 hours

The swell will hit the shores in 111.1 hours, which means 4.6 days. In four and half days, the swell we have been tracking might just bring pristine surfing conditions to our local spot.

Understand how waves are formed. Learn the difference between ground swells and wind swells.

Get the best surf forecasting books.

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