Learning to use surf forecasting websites and information to accurately predict when to go surfing is a skill that must be developed with time and experience. Your surfing will only get better if you go at the right time and place so you're practising in conditions that suit you!
In this post, I'll explain some of the key elements of a surf forecast, using a Magicseaweed forecast from Sandend, Scotland as an example, and hopefully give you a boost as you jump into surf forecasting. Yeehaa!
What is swell?
Swell is kinetic energy that has transferred into the sea by wind blowing over the water. This creates waves moving away from the storm that caused the wind, like ripples in a pond. This swell moving into shallow areas of water is what makes the waves we surf.
Surf forecasting websites get the data they use to measure the elements of a swell from wave buoys and weather stations. They then process this data with their algorithms to make a prediction on the waves that will arrive at shore.
Swell height
Simply, swell height is the size of the swell, measured in feet or meters. This means the distance a swell moves a wave buoy up and down in the water as it passes, and is normally calculated as an average in a collection of swell waves to give a good indicator of the average swell height.
Swell height is not the same as wave height, as there are a number of other factors that affect the size of the wave that breaks at the beach.
Swell period
Swell period is the gap between each wave in a collection of swell, and is measured in seconds. Or, you could say the number of seconds that pass between each wave.
There are two main types of swell, ground swell, with a wave period of about 10 seconds or more, and wind swell, with a wave period from 1-9 seconds. The reason for this difference is the distance travelled by the swell (the fetch) before it reaches the shore.
Ground swell
If the swell has travelled the breadth of the Pacific Ocean for example, it will have a much higher period as the swell has had time and distance to organise itself. Swell periods of close to 20 seconds are not uncommon! A high swell period can result in a wave height at the beach much higher than the swell height forecast.
Wind swell
On the other hand, if the swell is created by a storm relatively close to shore, the distance travelled is short and the swell period will be low and the waves unorganised and often 'messy'. Generally speaking, the higher the period the better, although there are always exceptions depending on the spot.
Here in Cullen and on the Moray Firth, the fetch is limited by the size of the North Sea, so we receive a mix of ground swell and wind swell. It's very rare to see a NE ground swell above 13 or 14 seconds.
Swell direction
To make waves at the beach, the swell needs to be heading towards it!
Some longer period swells can refract or bend around obstacles to arrive at the spot in question, but as a general rule, you want to see directional arrows pointing at your chosen spot on the forecast.
The angle of a swell can make a big difference to how a wave breaks. Imagine a solid built up sand bar - if the swell is hitting it directly it may well cause 'closeouts' or waves that break all at once and offer no green 'face' to surf along. The same spot might offer fast steep walls to surf along if the swell was arriving at an angle.
Tides
Another important factor to consider is the tide. The tide changing results in deeper or shallower water at different areas of the beach and this affects the way the wave breaks as the swell approaches shore.
As a general rule, you can expect mellower sloping waves at high tide as the wave breaks in deeper water, and steeper pitching waves at low tide as the wave breaks in shallower water. This is very dependent on the shape and slope of the beach and sandbanks though, and varies from spot to spot. For example, our local spot Sandend has a much more gradual slope to its beach than Cullen - this has important implications for the waves at different stages of the tides.
Wind direction
The last important factor to cover is wind direction.
Onshore wind
An onshore wind blows from behind the wave towards the shore, this can make the wave crumble and spill over before it hits the shallow water it would have broken in, and so can reduce the power and result in 'mushy' conditions.
It also creates chop and small waves that interfere with the main swell - 'messy' conditions.
Offshore wind
An offshore wind blows from the land to the sea, smoothing out surface chop and holding the wave face up for a moment before it breaks, often resulting in more powerful steep waves and picturesque conditions.
Too strong an offshore though makes for difficult conditions as the wind fights you when paddling into a wave and blows spray in your face . Very strong offshores are not suitable for beginners or paddleboarders if intending to go 'out back', beyond the breaking waves.
Wave height / Star rating
All these factors are combined in the surf forecasting website's algorithm to create a prediction for the height and quality of waves breaking at the beach.
Magicseaweed shows wave height and a star rating. While this can be useful as a guide, if you can learn to understand the different elements you will be able to make better informed decisions and sometimes catch things that Magicseaweed misses!
Armed with that information, check the surf forecast before you head to the beach and try to decide what you expect the surf to be like - you won't get it right all the time!
But over time you'll build the combined knowledge of how conditions affect your local spot and what the different elements of the surf forecast mean for the waves there. This is a big part of what surfers mean when they say 'local knowledge'.
You might find it helpful to keep a 'Surf Log' of what the forecast showed and what the conditions were really like. Pretty soon you'll be able to glance at the forecast and know when to run out the door and when to kick back with a beer!
