1 metre of swell, a 12-second period, an easterly wind at 5 knots, an outgoing tide… On paper, you have four figures. For a surfer who knows how to interpret them, they already tell much of the story of the session ahead.
The first rule is never to look at a parameter in isolation. 1 metre of swell doesn't automatically mean 1 metre waves at the shore. The period, swell direction, spot exposure, seabed, wind and water depth will transform that swell before it reaches your board.
It's precisely this combination that turns a basic marine weather forecast into a proper surf forecast.
Surf forecasts: the 5 key parameters to check first
To quickly decide whether a session is worth the trip, check the parameters in this order:
| Parameter | What it tells you | What to look for |
|---|---|---|
| Swell height | Swell size offshore | A size suited to your spot and ability |
| Swell direction | The angle the swell arrives from | A direction the spot can pick up |
| Period | Swell energy and spacing | A period suited to your ability |
| Wind | Surface conditions and how the waves break | Light winds or a light offshore wind in many situations |
| Tide | Water depth at the spot | The right window for that particular spot |
The classic mistake is to look only at the forecast height. Yet two days showing “1 m” can have almost nothing in common.
A 1 m swell at 7 seconds can produce relatively weak, closely spaced and messy waves. With 1 m at 15 seconds, there's considerably more energy available: the sets can be more defined and the spot much more challenging. A long-period swell travels more efficiently than a short-period swell.
The HawaiiSurf tip
Never choose your session based solely on the “wave height” line. Start by looking at these together: height + period + direction, then factor in the wind and tide. This habit helps avoid plenty of nasty surprises.
1. Understanding swell height and actual wave size
Swell and waves: they're not the same thing
Swell is an undulation that travels across the ocean. While it's in deep water, it doesn't necessarily look like the waves you see breaking at your favourite beach break.
As it approaches the coast, this energy gradually interacts with the seabed. The wave slows down, steepens and eventually breaks.
That's why a forecast of 1.20 m of swell absolutely does not guarantee 1.20 m waves at the peak.
The result depends, among other things, on the period, swell direction, bathymetry, coastal exposure and seabed type. Two neighboring spots can therefore have very different wave sizes even when they are theoretically receiving the same swell.
Exposed or sheltered spot: a major difference
A spot facing directly into the swell picks up more energy. A spot sheltered by a headland, an island or a different orientation can, on the other hand, filter out some of the swell.
That's what makes sheltered spots appealing on big days: when an exposed beach break gets too big or closes out all the way across, a more sheltered bay may receive a toned-down version of the same swell.
So the question isn't just “how many meters?” but “how many meters, from which direction, at which spot?”
2. Swell direction: knowing whether your spot will pick up the swell
A swell comes from a particular direction: west, northwest, southwest, etc. Apps may also express this in degrees.
Imagine a beach facing directly west. A swell arriving almost head-on will generally deliver more energy than one arriving at a very oblique angle.
But real coastlines are never just straight lines. Headlands, bays, islands, breakwaters and the seabed can refract or block some of the energy.
How can you learn the ideal swell direction for your spot?
The most reliable method is surprisingly simple: observe.
After each session, note:
- swell height;
- period;
- direction;
- wind;
- tide and water level;
- wave size observed at the peak;
- actual quality of the session.
After a few weeks, you'll start to identify your spot's “recipe.” This observation-based approach is also recommended for understanding how it works at different tides.
Our team's take
A screenshot of the forecast alongside a photo of the spot taken when you arrive is worth much more than a vague memory like “it was good at 1 meter.” Build your own log: it's one of the best ways to learn how to forecast conditions at a spot.
3. What swell period do you need to surf?
Period, the number beginners underestimate
The period is the time between two successive wave crests, measured in seconds.
The longer it is, the more efficiently the swell can carry energy. That's why two swells of the same height can produce very different sessions.
As a practical guide:
| Period | General interpretation | What to expect |
|---|---|---|
| 5 to 7 s | Very short-period swell | Closely spaced waves, often disorganized |
| 8 to 10 s | Short to medium period | Surfable, moderate power |
| 11 to 13 s | Good period | Better-organized sets and more energy |
| 14 to 16 s | Long-period swell | More powerful waves, more pronounced gaps between sets |
| 17 s and + | Very long period | Lots of energy; the spot can respond dramatically |
These values are guidelines, not a universal quality rating. A short-period swell can deliver a fun session on the right sandbank, while a long period can make a spot too powerful for your ability.
Why 1 m at 8 s isn't the same as 1 m at 15 s
This is probably the most useful example to remember.
With 1 m at 8 seconds, generally expect a less energetic swell that is more affected by local conditions.
With 1 m at 15 seconds, the ocean carries much more energy towards the coast. The seabed can then focus that energy and produce sets noticeably bigger than the “1 m” figure might suggest.
So never automatically equate swell height with the height of the waves you'll surf.
Is a long period always better?
No.
For an experienced surfer looking for powerful waves, a long period can be very appealing. For a beginner, however, it can turn a seemingly manageable swell height into demanding conditions.
It can also make some spots more intense: more powerful sets, stronger currents, heavier shorebreak or a tougher paddle out through the breaking waves.
4. Offshore, onshore and side-shore winds: how do you read them?
Wind directly affects the surface and shape of the waves.
Offshore wind: from land towards the ocean
Offshore wind blows from land out to sea. When it stays light to moderate, it can smooth the water's surface and hold up the wave's lip before it breaks.
These are the conditions you're looking for in many situations.
But “more offshore” doesn't mean “better”. Strong offshore wind can hold up the lip too much, throw plenty of spray at you on take-off and make it harder to get into the wave, especially on a low-volume board.
Onshore wind: from the ocean towards the beach
Onshore wind blows towards the coast. As it picks up, it creates chop and generally makes the waves less organised.
That doesn't mean a light onshore wind rules out a session. With a good swell and little wind, the waves can still be perfectly surfable.
Side-shore wind: watch out for drift
Side-shore wind blows parallel or almost parallel to the beach. Beyond affecting wave quality, it can quickly push you along the spot and force you to keep repositioning.
Take a look wind direction and strength, but also the gusts and, above all, how they change throughout the day.
The HawaiiSurf tip
On the Atlantic coast, the morning window is often watched closely because the wind can be lighter before thermal effects develop. That's not a hard-and-fast rule, though: trust the forecast's hourly changes rather than automatically assuming that “mornings are always better”.
5. High tide or low tide: when should you surf?
There's no universally best tide.
The tide changes the water depth above the seabed. And it's precisely the interaction between the swell and the seabed that turns the swell into a breaking wave.
At a beach break
On a sandy seabed, sandbanks shift with storms, currents and the seasons.
A sandbank can work perfectly at mid-tide and become too deep at high tide. A few weeks later, after several swells, its shape may have changed.
That's why beach breaks need regular observation.
At a reef break
The seabed is much more stable, so the spot's behaviour is generally more predictable. However, water depth becomes an obvious safety concern on shallow reefs.
The tidal coefficient matters too
A high tidal coefficient means a large tidal range. The water level changes more between low and high tide, which can quickly change how the spot works and strengthen certain currents.
Rather than remembering “this spot works at high tide”, try to learn something more precise:
“This spot works at this water level, with this swell direction and size.”
That's much more useful.
6. Primary and secondary swell: the detail that explains some unusual sessions
Advanced forecasts sometimes show several swell trains.
The primary swell generally represents the dominant component. A secondary swell can arrive from a different direction and with a different period. The two can overlap and change the water conditions. Surf-Report distinguishes these components in its forecasts.
You might find a clean primary swell coming from the right direction, accompanied by a second, shorter-period swell coming in at an angle. On paper, the height looks great; in the water, the peaks look less consistent.
For an initial read, focus on the dominant swell. When your observations don't match what you expected, check the secondary components.
7. How do you combine swell, period, wind and tide?
This is where the forecast gets really interesting.
Let's take a hypothetical situation:
Swell: 1.2 m — period: 13 s — direction: west/northwest — wind: easterly 5 knots — tide: rising.
Height alone doesn't tell the whole story.
At 13 seconds, the swell already carries significant energy. If the spot picks up west/northwest swell well, it can receive solid sets. A light easterly wind will be offshore on a beach facing west. You then need to work out whether the sandbank will work at the water level during your chosen session window.
At another spot sheltered from this direction, the same forecast can produce much smaller waves.
The 5 question method
Before heading out, always ask yourself:
-
Does the spot pick up swell from this direction?
-
Does the combination of height + period suit my ability?
-
Will the wind be favorable when I'm actually in the water?
-
Is the water level right for the spot?
-
Do live observations confirm the forecast?
If you can answer these five questions, you've already moved beyond a basic reading of a weather app.
8. Which conditions should you choose for your ability?
A “good” forecast depends on the surfer.
| Profile | Conditions to look for | What to watch out for |
|---|---|---|
| Beginner | Small waves, light wind, well organized conditions | Long period, currents, shorebreak |
| Intermediate | Moderate swell, manageable period, clean wind conditions | Bigger than average sets |
| Advanced | Conditions suited to your session goals and the spot | Power, currents, waves too big for the spot to handle |
When you're starting out, a small, clean swell is generally much better for learning than a powerful day. You'll catch more waves, work on your positioning and save enough energy to practice your take-offs.
Your choice of board also makes a huge difference. A board with enough volume and good stability makes paddling, positioning and catching waves easier, especially when you're starting out or the conditions lack power. Choosing from surfboards suited to your ability and the conditions helps you find the right balance between volume, stability, maneuverability and performance.
9. Match your gear to the forecast conditions
Reading the forecast also helps you get the right gear ready.
Board and fins
In small, weak waves, a board that generates speed easily will often be more fun than a demanding shortboard. A fish, a groveler or a board with more volume will generally help you catch waves earlier and maintain speed through softer sections.
When waves get hollower or faster, control and grip become more important. Your choice of fins then directly affects how the board handles: depending on their size, shape and setup — twin, thruster or quad — they can favour manoeuvrability, speed or hold through turns.
Matching your surf fins to the conditions and your board helps you fine-tune your surfing without necessarily changing boards every time the waves change.
Leash: match it to your board and the conditions
Your leash should above all suit your board, your build and the forecast conditions. The length and thickness you need for a small summer session won't necessarily be the same as for more powerful waves. Remember to regularly check the cord, attachments, swivel and rail saver too: waiting for a worn leash to snap in a heavy set is a bad way to find out it needed replacing. If yours shows signs of wear, choose a surf leash suited to your board and the way you surf before heading back into the water.
Water temperature and wind
A great forecast doesn't guarantee a comfortable session. Water temperature, air temperature and wind all have a big impact on how cold you feel, especially during longer sessions or when the wind picks up.
The right wetsuit lets you stay in the water longer without unnecessarily sacrificing mobility. Depending on the season and water temperature, you can opt for a 3/2 mm in relatively mild conditions or something thicker when the water gets colder. Your choice of neoprene wetsuits should therefore take temperature into account, as well as the wind forecast and how sensitive you are to the cold.
10. The most common mistakes when reading a surf forecast
Confusing swell height with wave height
This is the number one mistake. A swell measured offshore still has to interact with the coastline before it becomes a surfable wave.
Ignoring the period
“1 metre tomorrow” means almost nothing without the period.
Thinking a longer period is automatically better
It mainly means more energy. For some spots or skill levels, that can be exactly what you don't want.
Assuming offshore winds are always perfect
Light offshore winds: often excellent. Strong offshore winds: sometimes tricky.
Applying the same tide rule everywhere
Two neighbouring spots can need completely different water levels.
Looking at the day's forecast rather than the forecast for your session time
A day can start glassy, turn offshore, then end with strong onshore winds. What matters is the window when you'll actually be in the water.
Blindly trusting a rating or stars
A rating combines parameters according to a model. It knows neither your skill level nor the exact quirks of the sandbar that day.
Use ratings as a shortcut, never as a substitute for analysis.
11. The 5-minute routine before loading up your board
Here's a quick routine to follow before every session.
1. Look at the swell
Height, period and direction. Always together.
2. Check how conditions are changing
Is the swell building or dropping? Is the period changing? A session at 8 a.m. and another at 2 p.m. can be radically different.
3. Analyze the wind hour by hour
Direction, average speed and gusts.
4. Factor in the tide
Look for the window when the right water level for the spot lines up with the best wind.
5. Check in person or with a webcam
Forecasts are still models. A recent webcam feed or a look from the dunes shows you what's really happening: set size, frequency, actual wind, current, crowds at the peak and the state of the sandbar.
This final check is especially useful at beach breaks with shifting sandbars.
The HawaiiSurf tip
Don't just look at the best waves on the webcam. Watch for several minutes. Try to spot a full set, then see how long the wait is before the next one. You'll get a much more realistic idea of the session than from a screenshot taken at the best moment.
12. Learning to read your spot beats chasing the perfect forecast
Apps are getting very good, but no raw data can replace knowing a spot.
Two surfers can look at exactly the same model and make two different decisions. The one who knows the beach knows that less swell gets in from that direction, that a sandbar works at a certain water level, or that the forecast wind usually shifts earlier in that area.
That's when reading forecasts becomes a surfing skill rather than just a weather check.
Start with five variables: height, period, direction, wind and tide. Then always compare the forecast with what you actually find in the water.
Session after session, the numbers gradually stop being abstract. “1.2 m at 13 seconds from the northwest, light offshore wind and mid-tide” eventually brings a very clear picture to mind.
And that's exactly when you really start to know when to load up your board.
