Reading the wave forecast correctly is not that easy, but it is important! Not everyone is lucky enough to live right by the sea and simply check out the window in the morning to see if the waves are running. There is often so much going on at spots with beach cams that there is little left of the feeling of freedom when surfing. To avoid sleepless nights – for fear of missing the best swell – and to save you unnecessary trips to the beach, there are surf forecasts.
But you have to be able to read them properly!
Whether you’re a budding wave junkie, already check forecasts regularly or are still in the middle of kook status – here you can find out what really matters. So you’ll know when it’s worth setting off – and when you’d better stay put.
The most important things in a nutshell:
- To predict good waves, you essentially need information on wave height and direction, the period of the swell and the wind direction and speed.
- But it’s not just about weather data! If you know other conditions such as tides, sea bed structures and local wind phenomena, you will know whether the surf spot is suitable for surfing.
- Wave energy provides a better estimate of how powerful the waves are than just wave size and period.
The key factors of a wave forecast
Every wave forecast is based on several factors that influence each other. Here are the most important ones:
- Wave height
- Period
- Swell direction
- Wave energy
- Wind force
- Wind direction
- Tides
Wave height
The wave height is given in feet (ft) or meters (m) and describes how high a wave is in the open sea – i.e. before it hits land or breaks on the coast. This data is recorded by buoys that float on the sea and register vertical movements. The difference between the highest point of a wave (wave crest) and the lowest point (wave trough) is the measured wave height. In wave forecasting, we should therefore be talking more about swell size and not wave size.
One example
At a wind force of 6 (25 to 31 miles per hour (mph) or 22 to 27 knots (kn)), waves of 13.5 to 19 feet (ft.) are created on the high seas. However, this does not mean that these waves break at exactly this height at your surf spot – and this is where it gets exciting for surfers: because the actual wave height at the surf depends on several factors:
- Water depth & substrate: A wave hits the sea boulder, loses speed and thus becomes steeper – and eventually breaks. Whether it breaks hollow, dull or fast depends heavily on the spot or seabed.
- Swell period: A long period brings more energy, so that the wave breaks stronger and often higher.
- Direction of the swell: If the direction of the swell reaches the spot from a favorable angle, the energy can develop optimally.
- Local conditions: Tides and subsurface structures such as sandbanks, reefs or harbor walls can strengthen or weaken the waves. But local wind dynamics also have an influence on the wave height on the coast.
According to the forecast, a 13.5-foot wave can therefore only reach waist-high in the surf – or break twice overhead (double overhead). The actual wave size at the depends on how the factors mentioned above interact. It is important to understand how ocean waves are generated in order to understand the information in a wave forecast and to link it correctly with local knowledge.
Wave period
The period (also swell period, wave period or interval) is the time interval between two consecutive waves in seconds. A low wave period does not mean you surf a lot of waves. The shorter the intervals of a wave set (group of waves), the more chaotic and messy they are. Longer swell periods indicate a long-lasting wind during the formation of waves. This in turn means that the waves have more energy and are best suited for surfing! As a rule of thumb:
- Under 8 seconds: Unorganized wind swell that forms not far from shore and barely has time to build up. Breaks chaotically and is less surfable.
- 8 to 10 seconds: Unorganized wind swell, creates powerless, less unorganized breaking waves. Therefore usually difficult to surf.
- 11 to 15: Moderate groundswell provides enough energy in the set to deliver organized and powerful waves. They are not perfect, but are surfable.
- over 15 seconds: Ground swell that originated far offshore and had plenty of time to build up the waves. Therefore, very powerful and ideal for surfing.
Kilojoules (kJ) – wave energy
Although the wave strength is determined by the wave size and wave period, both units are not always suitable for comparing different waves.
Two examples:
Let’s compare two waves: Both are 4 feet high, but one has a period of 8 seconds, the other of 15 seconds. It is already clear here that the wave with the longer period transports significantly more energy and is therefore more powerful.
It becomes even more exciting when we compare a 4-foot wave with a 12-second period with a 3-foot wave with a 16-second period. In this case, the strength of the waves can no longer be assessed by height or period alone – here the wave energy, measured in kilojoules (kJ), is the more meaningful indicator. It shows how much power is actually in the wave.
For orientation: According to surf-forecast.com, at least 100 to 300 kJ are required for a longboard session, while you can take your mid-length or shortboard into the water at over 300 kJ.
The swell direction
The direction from which the swell comes is called the swell direction. It is specified either in cardinal points such as north (N), northwest (NW) or as an angle in degrees: 0° or 360° stands for north, 90° for east, 180° for south and 270° for west.
How well a swell direction works at a surf spot depends heavily on the orientation of the coast. If the swell hits the coast at an unfavorable angle, the waves can be weakened, barely break or not arrive at all.
You can find out more about how swell directions behave at your spot in our blog article on the wave refraction of ocean waves.
Wind strength and direction
- The wind is one of the decisive factors for the quality of the waves – it can perfect them or destroy them completely. Several aspects play a role here: firstly, the wind force (also known as wind speed), which is usually specified in miles per hour (m/s), meter per second or knots. Secondly, the wind direction is decisive – similar to the swell. As wind is a very dynamic factor that can change constantly, the direction is often simplified in practice as onshore, offshore or sideshore.
Important: The wind direction always describes the direction from which the wind is coming. Here is an overview of the most important wind types and their effects:
- Offshore wind: Blows from the land out to sea and smoothes the water surface. This creates clean waves with a clear face that build up slowly and evenly – dream conditions for surfers!
- Onshore wind: Blowing from the sea towards the land. This wind makes the waves chaotic, unpredictable and often unusable for surfing – a nightmare for many surfers.
- Sideshore wind: Blows parallel to the coast. Depending on the spot and swell direction, this wind can either smooth out the waves a little or make them more turbulent. Effect strongly dependent on location.
- Cross-offshore wind: A lateral offshore wind – i.e. slightly diagonal from the land – also keeps the waves open for a long time and ensures good conditions, even if they are not quite as clean as with pure offshore.
- Cross-onshore wind: Slanting onshore wind – slightly better than classic onshore, but still usually causes turbulence on the water surface and shorter breaking waves.
A light offshore wind is ideal in most cases. Strong winds, on the other hand – regardless of the direction – can severely deteriorate the surfing conditions.
Rule of thumb for the forecast:
At wind speeds below 5 knots (approx. or 6 mph), the wind has little effect on the water surface – you can usually disregard it in the forecast.
Onshore winds above 5 knots are visibly noticeable and make the waves choppy if there is no wind protection at the surf spot.
Sideshore winds usually only have a noticeable effect on the wave structure from around 11 knots – here too, a lot depends on the particular spot.
tides
The tides – i.e. high and low tide – have a decisive influence on surfing conditions. They change the water level and therefore also how waves break at a particular spot. How strong this effect is depends primarily on the ground of the spot (sand, reef or rock) and its orientation.
Important to know:
Not every surf spot works equally well at every tide. Some work best at high tide, others only at low tide or in transition – i.e. mid-tide. Some spots even only work in a very narrow time window around high or low tide. Therefore:
- Local knowledge is worth its weight in gold. Ask other surfers, observe the spot at different times of day or use experience reports from surf apps.
- Tide charts are a must in order to plan your session correctly – especially at new spots.
- Swell height and tide work together: If your home break is running perfectly at 5 ft. swell and tide, it may be surfable well before high tide if the swell is smaller. Conversely, a spot that is running at low tide may even be overwhelmed by a large swell.
In short: the best surfing time depends not only on the swell forecast, but also on the tide. Reading both in combination gives you a clear advantage when planning your session.
Other factors in a wave forecast
In addition to the factors mentioned above, there are other details that can influence your session:
- Main swell: also known as the main swell or primary swell, is usually the most powerful and relevant.
- Secondary swell: Secondary swell can also change the conditions – positively or negatively. If waves from different directions meet, more chaotic or complex wave formation can occur.
- Wind gusts: Can deviate greatly from the wind speed and briefly influence your surfing experience. e.g. roughen the water surface for a short time, make waves close faster or throw you off balance.
- Sunrise and sunset: Important for dawn-petrolers! Helpful if you are planning a sunrise and sunset session.
- Surf guides and spot description: Additional information about the spot can be particularly useful and provide details about the seabed, the conditions under which a spot works well (including wave size, swell direction and ideal tide conditions), the wave type, paddle intensity (current) and the vibe in the water.
- Air and water temperature: Not only important for wetsuit selection, but also helpful for good-weather surfers.
How does a surfing forecast work?
It takes a lot of data and computing power to make your surf forecast look the way you know it. Weather stations, satellites and buoys collect weather data such as wind direction, wind strength and air pressure around the clock.
This information is fed into global wave models such as the GWM (Global Wave Model), the ECMWF (European Center for Medium-Range Weather Forecasts) or the NOAA (National Oceanic and Atmospheric Administration) models. They use these to calculate swell direction, periods, wave sizes and wind conditions.
Regional models such as SWAN (Simulating WAves Nearshore) are even more accurate.
They take into account local conditions such as coastlines, subsoil or islands – in other words, everything that influences the wave locally.
Most surf forecasts today use hybrid models, i.e. a combination of global and regional data. This gives you the most accurate forecasts possible – for exactly the session you’re hoping for.
How reliable is a wave forecast?
Surf forecasts are based on complex weather data and model calculations – but they are never 100% accurate. The level of detail and reliability varies depending on the model. Generally speaking, the more frequently the data is updated and the more computing power behind it, the more accurate the forecast.
However, individual forecasts can vary – so it is worth comparing several wave forecasts with each other. This will give you a more realistic picture.
And very important: local knowledge is often the key. Because what looks promising on the forecast can have a completely different effect in reality – e.g. due to the shape of the coast, local winds or currents.
Remember: The further into the future the forecast is, the less accurate it will be. Forecasts for the next 24 to 48 hours are usually quite reliable – anything more than that is more of a rough guide.
Don't rely on wave ratings
Many forecast sites use their own algorithms (rating systems) – such as stars, colors or scores – to quickly assess surfing conditions. Sounds practical, but is often too general and unreliable to safely plan a session. It is much more important to know the characteristics of your surf spot – because they determine whether the conditions are really suitable.
Local knowledge of the surf spot
Every spot has its own peculiarities that even the best models are often unable to depict. If you know them, you can get more out of the forecast – or save yourself the trip to the beach. Pay particular attention to the following points:
- Tidal window and tidal sensitivity: Not every spot runs at every tide. Many only work in a narrow time window. If you know the timing, surf at the best time of day.
- Swell size and direction: Some spots only work when the waves are the right size and direction! Pay attention to how the waves behave in different conditions.
- Sandbanks that are constantly changing: Especially at beach breaks, sandbanks change regularly due to swells, tides and currents.
- Swell filtering: Not every swell actually arrives at the spot. Shorelines, offshore islands or underwater structures direct, block or filter waves. Those who are familiar with the refraction and diffraction of ocean waves can better assess when and where a swell will work.
- Local wind phenomena: Sea breezes, thermals or valley winds are often not accurately predicted. What was announced as offshore can suddenly become sideshore or onshore on site. Dunes, cliffs or forests can provide additional protection from the wind.
- Currents and other dangers: Currents aren’t always bad – they often get you into the line-up quickly. But they are rarely mentioned in forecasts, nor are sea urchins, weever fish or other local dangers.
If you understand a spot, you can turn an “okay” forecast into a perfect session – or know when it’s not worth going to the beach. There is no substitute for local knowledge.
What types of wave forecasts are there?
Wave forecasts are not only presented in different formats, but the data is also collected differently. The most common types are:
- Graphical swell maps: These maps show the swell height, direction, and period in a visual representation. They are particularly helpful for identifying large-scale swell patterns and estimating which regions can expect good waves.
- Tabular forecasts: This format is found on most surf forecast websites. Data such as wave height, wind direction, wind speed, and tides are presented in tabular format, allowing you to quickly access the most important information at a glance.
- Algorithm-based surf ratings: Some platforms provide an overall rating for a surf spot—often in the form of stars or a point scale. These ratings combine several factors such as swell, wind, and tide to provide an assessment of whether the conditions are surfable or not.
- Live data and beach webcams: Wave forecasts are calculated not only through wave model predictions, but also through automated observations from beach webcams. This integration provides real-time data from surf spots based on actual prevailing conditions, such as current wave heights and wind conditions, directly from the source. Webcams also provide a visual impression of what the conditions are actually like on-site.
Each of these forecasting methods has its own strengths, so it may be useful to compare multiple sources to get the most accurate picture of wave conditions.
What is the best app or website for wave forecasts?
The best surf forecast app or website depends on what’s important to you: Are you looking for detailed wave data? Do you want to keep an eye on wind conditions? Or do you just want to quickly check the webcam in the morning to see if the spot is worth the trip?
For good waves, you need a combination of the wave forecast and local knowledge – and ideally an app that provides you with all of this in a clear format and pays attention to how waves behave in certain conditions. Here are some of the most popular and reliable providers:
- Surfline: One of the most well-known platforms worldwide. Offers detailed wave forecasts, live webcams, spot reports, and premium features like session replay.
- surf-forecast.com: Very popular for detailed swell information, including wave energy information. It also has a handy wave finder and an alarm function when your favorite spot promises good conditions.
- Windy: Perfect for anyone who also wants to keep an eye on wind, weather, and currents. Offers a very powerful graphic representation – ideal for wave and wind data, with clear graphical representations, including currents.
- Windfinder: Focuses on wind forecasts – with the Superforecast, you get hourly updated wind and weather data.
- Windguru: Offers extensive weather and wave data in various table and graph formats. Ideal for advanced users who like to delve a little deeper into the subject.
Comparing several providers can help you get the most accurate forecast, especially regarding winds. Since winds change frequently, having up-to-date data can be worthwhile. The provider Magicseaweed no longer exists, having been acquired by Surfline in 2017 and has been unavailable since 2023.
Now you know what to look for when reading the wave forecast and can get the most out of your surf sessions and improve your local knowledge at your home break.
Summary
Swell direction, wave height, period, wind, and tides are not the only key factors when it comes to predicting good waves. Take your time and learn how local factors like sandbanks, seafloor type, or natural wind protection can greatly impact wave quality. Bottom line: Ignore Algorithm-based (star)ratings on their own — local knowledge is the key to score good waves!
