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Combining Swells at the Pipeline

I wrote the other day about the issues of swell in combination and the importance of reading the full forecast to best understand local conditions and the 2012 world title showdown at the Banzai Pipeline couldn’t have provided a more vivid example of the effect on the surf. While all eyes were focussed on the arrival of a modest but long period NW swell providing the best opportunity of the last few days of the window the story was complicated by a high pressure system creating a weak easterly fetch. This manifested not only in strong local winds, but importantly a clearly visible NE mid period swell that had a […]

North Atlantic 950mb Super Storm

Check out this chart issued by the NWS Ocean Prediction Center. It shows the developing North Atlantic 950mb low that set to bring huge surf to Europe over the weekend of the 15th/16th December. The outline, matching the size and shape of the continental US, shows just how huge the storm is – with an fetch stretching from Portugal to the Labrador sea: Or for a slightly clearer view of the coast here’s the same storm on our charts: The southerly Jetstream means swell will develop futher South than has been typical of recent storms, bringing larger swell to the coasts of Portugal and central Europe and opening up less […]

Combining Swells Issue

Some feedback on the new forecast highlights cases like this where the basic overview is dramatically different – it’s worth explaining because it highlights a considerable issue with the old layout that helps explain why we’ve made the change. You can see below an image showing the differences for Cape Town this week: On the face of it a 50% larger call on the old forecast than the new one. In fact the situation is pretty simple – in both cases the model data is the same but the difference is the way we interpret the fact that there are actually two swells running: A solid SW ground swell and […]

Forecast Period vs Wave Buoy Period

We get regular emails telling is that the forecast swell period is wrong. ThisĀ assessmentĀ 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 […]