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 marked effect on the waves.

(c) Kirstin ASP / www.vanstriplecrownofsurfing.com

While there were the expected NW bowls wrapping onto first reef the NE swell was clearly visible moving perpendicular to the line up. As this crossed up with the incoming longer period swell it created two or three separate peaks on the same wave and a shifting takeoff making for the trickiest conditions over the shallow reef. The effects sometimes positive, adding size and shape to a backdoor wave  (which would have been less likely to have offered scores in a single swell with this much west in it) and frequently not, creating close out sections that could have otherwise been navigated.

This sort of combination of swells is, for most breaks around the world, the norm rather than exception – especially on beaches exposed to large open ocean fetch from a number of directions.

The same scenario gives rise to the sort of South/NW combination swells that can be so positive for beaches on the US West coast – creating a-frame peaks where straight handers might be more typical on a single swell alone.

Making the data you need to spot this sort of situation easily available was one of the drivers for modifying our forecast pages recently. Where, initially, a number of our visitors were confused by the listing of more than one incoming swell the reality is with this data you can dial down exactly the sort of waves you’ll see in an event like this:

MSW Forecast for Friday 14th at Pipe

We’re highlighting the NW swell as the dominant one here, it’s the one that prompted the call to competition, but clearly visible is a 5ft@10second NW swell in combination. Most surfers will be well aware that a swell of this sort of size is comfortably capable of creating head high+ conditions in it’s own right and it’s existence in the mix is pronounced as last night showed.

How to Use this Information

From our experience we’d suggest the following rules of thumb:

  • Predict the surf size based on the largest single swell.
  • Add a little to your size expectations if there’s a supporting swell (but definitely don’t expect two similar swells to double the overall size!)
  • Expect a ground swell with a low period wind swell to feel a lot like the confused conditions of the wind swell but with more power on the sets.
  • Expect waves from a combination of swells at around 45-90 degrees from each other to create more peaky waves, with a-frames on beach break under perfect conditions.
  • Look for locations that filter the combination of swells – for example tucked behind a headland that blocks the low period waves but allow the longer period swell to wrap in.

MSW Wind Chart showing the fetch increasing trade winds and creating the NE swell