A Little Help with Surf Forecasting

In the interconnected world we currently find ourselves in, it’s never been easier for humans to access information. Whether it be news, gossip, WSL rankings, iTunes terms and conditions or Donald Trump’s most recent tweet, pretty much anything is available with a few characters typed into a search engine. For the modern surfer, much is the same, the art of predicting surf conditions has become largely a matter of whether you have windguru on your iphone, which I'll concede is certainly handy...most of the time.

Some day however, curiosity may get the better of you as to why Magic Seaweed gave Wednesday’s forecast 4 out 5 stars when in fact the surf was total shite. How did they get it so wrong? Perhaps you’ll start wondering how in all hell that one punter always manages to score waves during prolonged periods of small swell or howling on shores? (Hint: Most of the time he’s lying). Regardless, when generic regional surf forecasts start letting you down, of if you want to be a real man or lady of the ocean it's probably time you started working things out for yourself.

First off: surf forecasting, and general synoptics (that's the study of weather patterns for the un-initiated) is not an exact science. I recall when I was studying Meteorology being told by a dower instructor that 'regional and local weather forecasts are only 100% correct 40% of the time'. Pretty poor odds. The number of variables when you start adding surf, to a weather forecast will throw that accuracy off even further.

Nevertheless, here are a few tips and definitions, mostly aimed at the beginner to intermediate surfer who wants to be a little more dialed in.

Good surf is generally governed by two macro factors. Swell and wind, each of which which are in turn defined by their direction, and intensity. A number of lesser factors such as tidal coefficient, ocean floor topography, coastal direction also play lesser roles.

For the purposes of this article we’ll focus on swell, wind and tide which without exception applies to all surf spots. The other stuff you’ll pick up through a roughly  50/50 mix of experience and bullshitting.

First up: wind. Generally speaking wind is generated by the uneven heating of the earths surface by the sun. Some areas get hotter faster than other areas which results in a low pressure. The air in the colder area with its higher pressure rushes in to fill the vacuum. Cold = high pressure. Hot = low pressure. The higher the temperature difference between two areas, the more likely that the resultant wind will be a strong one. Typically, those large storms that form out in the oceans that generate high winds are all an eventual result of unequal atmospheric heating.

When these high winds pass over the surface of large, deep bodies of water, they generate swell. It's important to note that at this stage it's not yet a surfable wave, but rather a lateral movement of water caused by the wind acting on its surface. Waves are a coastal phenomenon. If the wind is strong enough and the body of water large and deep enough, we get what's been popularized as ‘groundswell’. That is a large powerful swell that have been generated a long way from where they eventually reach a coastline and become waves. This is the difference between ‘windswell’ which has been generated near to the coast, in shallow water, by a fairly weak local wind, as apposed to 'groundswell' generated by say a cyclone spinning 100 mile per hour winds in deep water a few hundred kilometers off shore. In the first instance, bring your longboard, in the second, your 6'2" rounded pin.

Wave quality with regard to surfing is generally measured by two related, yet ultimately different criteria: Size and Period.

Swell size is as you may guess, is self explanatory: Simply put it's the vertical height of of the swell, measured in meters or feet from the base of the trough, to the crest of the wave. Bigger swell=bigger waves surely? Yes, but only to a certain extent.

Quality surf is also hugely dependent on something known as Period. Period is the time, measured in seconds, between consecutive waves in a swell. A swell with a small period of say 5 or so seconds will result in a messy, disorganized ocean. Probably with an abundance of surface chop all over the place and with little in the way of quality waves to surf. A longer period of say 12 seconds means a consistent clean swell with little in the way of chop or other surface disturbances.

If we refer to the earlier example of a tropical cyclone, let's say this particular one is 200 miles off the east coast of Siargao island in the Philippians way out in the central Pacific Ocean. Right near the eye of the storm, you can bet there is going to be some enormous swell, but due to it's proximity of to center of the weather system generating the swell, the period will be tiny. Giant surf all over the place, conflicting swell directions, and hundred per mile winds. Hardly a surfers wet dream. 200 miles west of that storm though, after all that energy has travelled and dissipated somewhat, with all the lesser and conflicting swells losing much of their kinetic energy,  it arrives (hopefully) as a perfectly groomed, big long period groundswell. Barrels at Cloud 9.

There are a number of types of weather phenomena that can cause the winds strong enough to produce large swells. The previous example was the extreme, a cyclone/typhoon/hurricane (which incidentally are all the same thing depending on which part of the world you're from) are the most violent weather phenomena on earth. But most large depressions (areas of low pressure that is...) and their resultant storms will create swell provided the atmospheric instability they generate is great enough. In the North Atlantic it'll be the large North Atlantic storms in the bay of Biscay that  bring the swell to Hossegor, Mundaka, and Peniche. In Jeffrey's Bay, it'll be a southern Atlantic cold front moving up the east coast of South Africa that'll turn on Supertubes. Even landlocked and usually waveless seas such as the Mediterranean can have the odd day of cooking surf in places like Tuscany in Italy winter when the Sirocco sets in.

A lovely example of this is on Hawaii's North Shore. If there's a big enough blizzard in Tokyo Japan, you can bet that a within a weak the swell that very storm generated is going to light up Pipeline, some six and a half thousands of kilometers away.

On to tides. Understanding what effect tide is going to have on surf conditions doesn't require as much processing as swell size, period and wind does, however most surf spots require a basic understanding tidal coefficients.

Ultimately, Tide is caused by the gravitational pull of the moon as it spins around us, and the sun as we spin around it. Both these celestial bodies in turn drag a giant chunk of our oceans towards their respective lunar and solar bodies as they go about their respective orbits. When the sun and moon are in alignment, we call that a spring tide. High tide will be exceptionally high, low tide will be exceptionally low, much like a manic depressant of their meds.

When the sun and the moon are on opposite sides of and earth is playing piggy in the middle, the gravitational pull of both sun and moon largely cancel themselves out. We call this neap tide. With a neap tide, typically there won't be much of a difference between high and low tide.

Certain surf spots around the world are very dependent on tide with some working on a high, or low tide respectively. Fortunately, forecasting tides for a certain spot is fairly easy, since the factors governing a tide aren't variable (we orbit the sun at a constant rate, and the moon orbits us at a constant rate), so pulling up a tide chart for an area is as simple as an internet search. Knowing which spot to check on high or low is a matter of experience more than anything else.

Broadly speaking, everyone who surfs has a general idea of when surf is going to be good and when it's not. While stuff like working out when it's going to be offshore, what season generally beckons swell, is largely a function of how well you know a particular surf spot, being able to accurately predict good surf to within a day (or even an hour or two if you really know your stuff) is a bit of an art form. If you master this art form, it can be one of the most rewarding aspects of our sport/lifestyle. After all, what's better than scoring sneaky great waves while everyone else gets hopelessly skunked you little pig you !