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The Drifter Journals

Reading manisha Ripples | The Art of Forecasting

“What creates the wind? Is it the breath of God? What creates the clouds?“Where do the great swells come from? And for what? Only that now it was time... and we'd waited so long.”

- Robert Englund / Fly, Big Wednesday

Swells come and go - it’s the nature of life. Sometimes it’s offshore and five feet, at others, it’s a one-foot onshore grovel.

Surfers live by the charts. A thousand apps and websites pour information to our fingertips and the days of surflore and oceanic wisdom have faded into the mists of time like so many elders. We no longer trace the path of seabirds, read the semaphore of cloud formations or give our lucky seaweed a hopeful squeeze.

The digital world has made life incredibly convenient for us, but it is far from infallible. Surf reports and forecasts are often written by faceless entities far from our local breaks, hypothesising on suppositions and pitching at a 60-percent average at best.

That said, our hats are humbly clasped in hand; forecasters do a sterling job of reading the signs and unfurling the formulae of wave prediction for our understanding. But there’s something to be said for a surfer who can check the lunar phase, gaze out to the horizon, lift a wetted finger to the wind and say, with absolute certainty, “tomorrow’s on.”To some, it’s second nature, but to most, the mystic language of tide charts, isobars, wave periods and significant heights is as foreign and unintelligible as the Baghavad Gita in the original Sanskrit.While meteorology takes many years to study and even more to fathom, there are a few telltale signs that offer we mere mortals at least a whisper of a clue. So if you want to be the salty, swarthy guru of your lineup, throwing down obscure pearls of wisdom for the uninitiated, take a read of our eight steps to Surf Forecasting 101:

Swell Growth

The first step is to peer into the future for a potential swell. Weather maps trace climatic pressure, mostly to assess onshore changes, such as rain and wind, but they also offer insight into swell growth. Isobars - the meandering web of lines on weather maps - show pressure systems in real-time. Meteorologists do extrapolate on these, but viewing the current and past charts will show you swell potential. If the lines are close, long and progressing in your direction, chances are that a swell is on the horizon. Loose lines or tight angles predict no swell or a fleeting and fickle pulse. Viewing a progression of these maps over a day or two will also offer the swell direction.

Photo: ©Magic Seaweed

Swell Direction

The best direction of a swell often comes down to local knowledge. Swell direction is measured in degrees or compass points (eg: NNW or westerly). As a huge generalisation, a swell direction at 45 degrees to a break is a good thing. If you’re on the beach looking at a left-hander, you want the swell to be coming towards you from a 45-degree angle from the left. The problem is, this only works for an absolutely machine-perfect set-up. Variations in the ocean floor, the shape of the coastline and offshore reefs can all create variations and refractions, energetic echoes that will push the swell in different directions and even greatly magnify smaller swells. For example, notorious Californian big-wave spots, Blacks Beach and Mavericks can be absolutely pumping, but five kilometres up the coast it will be almost flat. This is noticeable in a tight bay, where smaller swells will bounce off the coastline and shallower seabed and be magnified by the narrow geography.At a completely new spot, studying the isobars for swell direction can give you a ballpark, but it’s not until you get to know the break that you will really understand what swell direction is best.


Wind is what creates the waves. Far out to sea, the wind blows, picks up a chop and slowly engorges it into a swell. To make a decent swell, you are looking for three key factors. You want the wind to be blowing for more than 24 hours to gather enough force and organise the lines, you want a large fetch, or area across which the wind is blowing, and you want a decent wind speed.

When these factors combine and the isobars are heading in your direction, you can pretty much guarantee that swell is on the way. The last remaining factor is what is happening on land. Depending on temperature changes and storm fronts, the wind direction may change to onshore, crumbling what would otherwise be a nice four-foot swell.

Wave Height

Wave height is all-important, for obvious reasons. It also drastically affects the break. Seeing a three-metre swell doesn’t mean that you will have three-metre waves on your local break. The swell height is taken far out to sea, measured from peak to trough on the biggest sets. By the time it gets to shore, some of the energy may have dissipated, wind may have flattened the swell and you’re likely to only see 30 to 50 percent of the measured height. Too much swell can also be a bad thing. Waves break when the ocean becomes less than one and a half times their height. So a five-foot wave will generally break in 7.5 feet of water. Of course, breaks like Teahupo’o and other shallow reef breaks that appear dramatically from deep ocean completely blow this theory out of the water, so to speak. So again, local knowledge and understanding a break’s personality is also a key factor.

Wave Period

New swells are scattered, organic, disorganised and unpredictable. Over a day or two, they become more refined and, given enough time, they will gain increased period. This is the gap in seconds between successive waves.

A slightly pointless fact is that when multiplying the period by 1.5 you get the wave speed in knots. Knowing this is kind of irrelevant, but understanding that a bigger period creates more speed, and more speed creates more height is always a good factor to bear in mind. On the whole, a longer period of at least 10 seconds will make for a cleaner, bigger swell.

As with wave height, this is measured by buoys anchored far out into the ocean. Every country has its own buoy network, so you’ll need to Google to find the readings relevant to your local break.

Swell Types

Swell breaks down into two categories: windswell and groundswell.Groundswell is produced offshore over a longer period of time. This makes for cleaner, more organised and generally larger swell and what much forecasting is based on and concerned with.Windswell is more spontaneous, scattered and disoganised. Produced closer to shore by prevailing winds, it’s usually messier, smaller and short-lived, but it can produce conditions favourable enough to be worth paddling out.

Break Types

Most surfers will know the difference between a beach break and a point break. Hell, even Ohio State Buckeye quarterback punks know that. The soft sand floors of beachbreaks are constantly on the move, so you can never truly predict where the swell will break from week to week or how conditions will present themselves. Following swell and wind patterns can give you a fair guess, but again, local knowledge and regular checks to assess the size and position of sandbanks are the only way to go.Reef and point breaks are far more reliable and consistent. Chances are, good waves one year will predict a solid swell the next year under similar conditions.The refraction we mentioned before comes into play with these different types of breaks. Beach breaks are usually wide and open, so what you see is what you get. A reef or point can often refract swells, magnifying waves significantly.However, beach breaks will both benefit and suffer from a wider variety of conditions. With an extensive, open shoreline and numerous banks, numerous swell directions will deliver, but the break will be more wind-affected. Points and reefs are often dependent on specific directions of both swell and wind.

Weather & Tides

Last on the list of predictive markers are the real-time weather and tides. Seasonal temperature changes will alter prevailing winds. Bali’s trades blow onshore for several months, but mornings will still offer plenty of choice. Short story: you want the wind blowing offshore, from the land to the sea.

Tides can also have a huge effect on waves. Remember, waves break in water less than 1.5 times their height. It’s also worth noting that the fuller the moon, the higher the tide, for better or for worse, but the moon can play a key factor in predicting a good swell.

A solid swell may work perfectly through the low tide, but when it increases a couple of feet, the same break will look like a lake, despite there still being a reasonable amount of swell. Low tides can be dangerous though, exposing reefs and making your window for error far less. Likewise, low tide on beach breaks can often mean heavy, unrideable close-outs.

Tide movement also plays a part. You may have the same height of tide, be it incoming or outgoing, but the break will act very differently at these two times, depending on its formation.

Tide preference often comes down to the personality of an individual break. So for your first couple of days on a new break, observe your surfing times, check the tide tables and assess the break at different times of the day to find that tidal sweet spot.

If all else fails and the flat spell is driving you to consider taking up macrame, we’ve heard that burning your favourite board or sacrificing your first-born to the wave gods works wonders… joke folks, please don’t set light to your quiver or drown your children.

We hope this intro gives you a better overview of swell prediction. But of course, you’ll never know ‘til you get out there.


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