How Unusual is this Run of Giant Swell?

Here we go again. Strike three is on plan for the middle of the week. A slightly different angle but the same basic theme: Big swell, strong winds and high tides. Here we take a moment to look at how this winter's run of swell compares to the past few years.

Big storms in the North Atlantic in winter, it's hardly rare. So just how unusual is this recent run of giant swell? This last couple of months does seem to be setting climate records. The UK Met Office are calling December the "stormiest since 1969" and here in England rainfall records have been set this past month. The charts below show the number of days in December that exceeded 20ft+.

To understand complex phenomena you always have to simplify. Any discussion of whether this winter is 'better' or 'bigger' than the past is going to involve a statistical approach. There are inherent risks with this. It's tempting to look at average wave heights over the month. But two 10ft days aren't the same as one 20ft day. Likewise a glance at recorded maximums gives a great idea of one off events, but no hint to the consistency that most surfers are interested in. This approach we hope bridges this gap and provides an interesting analysis of this winter. The chart below uses the same analysis for January:

For both December and January you can see not just a standout number of days with large swell but how far south the largest waves are travelling or generated in comparison to the last few years.

At a glance this last run of swell is a definite standout. Boosted by a marked contrast between cold air from the north and warm air from the south a particularly strong, southerly jet stream has been incubating some giant storms. But it's not unusual to see weather phenomena grouped together like this: the larger scale forces that drive this more local weather can often sit in a semi stable state for longer periods of time and parts of the process can actually feed back positively into the system, increasing the likelihood of further events. That's to say the odds of each event aren't independent. It'd be reasonable to assume we're statistically more likely to see a huge storm form having already seen one, than had we been experiencing calm conditions for the last two months.

Secondly many periodic climatic patterns operate at a frequency that sits uncomfortably with our memories, let alone the ever shortening news cycle. At MSW we keep about 15 years of archived records, a blink in the eye of climate history and certainly not a timeframe that allows for serious analysis of long term trends. Besides an event can either be an anomaly OR a trend – it can't reasonably be both, despite many in the media attempting to conflate serious debate about climate change with the latest notable weather phenomena.

What must increase the odds of this exact combination being replicated in short term historic record are the huge tides that, by coincidence, have occurred with both the last huge swells. For Wednesday we're seeing a slight easing of these, but we're still in a larger spring tide range for most of Europe. This, coupled with a more southerly storm track and stronger winds to gale force at time will give no respite for our sand scoured beaches and coastal structures. There's almost certainly more damage and flooding to come. In addition this storm will run too far south to show much swell at all at Ireland's standout breaks, and yet hit almost directly those in France and Spain and with winds far south enough to disrupt even Portuguese big wave spots. Northern Spain will shelter Morocco from the bulk of the swell. All in all you are left with a huge swell but not much in the way of worthwhile surf at the breaks able to handle it. In reality this storm is for those surfers tucked away on normally swell starved coasts that will, no doubt, briefly light up for those not afraid of a little wind.

P.S. Storm #4 is on the charts for next weekend.