Swell Models

Computer swell forecasts drive the lions share of internet forecast sites and particularly MSW which was the first to bring free long range model data to surfers everywhere. Understanding how they work will hugely improve your ability to forecast the surf for your local beach.

Forecast Period vs Wave Buoy Period

We get regular emails telling is that the forecast swell period is wrong. This assessment is based, quite reasonably, on the regular differences between the model forecast and the numbers observed on a local wave buoy. However this difference doesn’t mean either is wrong. The explanation is that most wave buoys look at ‘average period’ of all swells where, more usefully, your forecast looks at peak period of each separate swell. The crucial thing to understand about model forecasting is we’re trying to simplify things in order to predict them. Most surfers know that swell height is the peak to trough size of the wave and that wave period is the time […]

28 Second Period Model Boundary Issue

UPDATE: 11th August 19.37pm (BST) The NOAA have explained the issue is related to the unprecedented sea ice retreat revealing a numerical issue with their model and are working on a fix. We’re working on deploying alternative data in the interim. UPDATE: 11th August 12.15pm (BST) We’re still seeing significant issue on the northern boundary of the model. We’ve taken steps to identify and remove the problem data from your local forecast page but this is an interim fix and won’t fix affected charts. Apologies for the ongoing issue. We’re seeing what look like erroneous results in the main NWW3 model product we use for our forecasts. A large long period swell […]

What is a Swell Model?

A model is just a way to define how something works and test out hypothetical situations. Something as simple as saying speed x time = distance gives us a very very simple model for describing how long it takes you to drive from home to the beach. Straight away we can use this model for a bit of forward planning. We know you live 60 miles from the beach, we know your van can only manage 30 miles an hour, so we know that it’ll take you 2 hours to get there. We’ve created a model and we’ve used it to predict what will happen. You might not have ever […]

The Model Grid

A swell model works by representing the whole globe as a grid of squares. It’d be impossible to ever calculate how every drop of water in the ocean will move and react and the whole purpose of a ‘model’ is to create a simplified view of things, the grid is part of that. Typically a swell model will split the globe up into squares between about 30-60 miles wide. This has a huge benefit, we can now calculate what every swell on every ocean will do with just over 80,000 squares in our grid – manageable for a modern computer. It’s worth understanding some of the implications of this for […]