How to read a surf forecast: swell, period, wind and tide

What swell height, period and direction really mean, why wind matters as much as waves, and how to pick the best session.

Why forecasts matter

Surf conditions change from hour to hour. The same beach can be perfect in the morning and unrideable by the afternoon, or flat one day and dangerously big the next. Learning to read a surf forecast helps you choose the right beach, the right time and the right board, and it is one of the most valuable skills you can develop as a surfer.

A surf forecast combines several pieces of information: the swell, which is the energy that creates waves; the wind, which shapes the surface of the water; and the tide, which changes how waves break on a particular beach or reef. Understanding each of these, and how they interact with your local spots, is the key to finding good waves.

Swell height

Swell height is usually given in metres or feet and represents the height of the open-ocean swell, often as the average height of the larger waves. It is not the same as the height of the waves breaking on the beach. Depending on the beach's exposure, the seabed and the swell direction, breaking waves can be bigger or smaller than the forecast swell height.

As a rough guide, small swells suit beginners and longboarders, while bigger swells are for more experienced surfers. Learn how your local beaches respond: some beaches turn a small swell into fun waves, while others need much more to break.

Swell period

Swell period is the time, in seconds, between successive waves passing a fixed point. It is one of the most important and least understood numbers in a forecast. Longer-period swells, generated by powerful, distant storms, carry more energy and produce bigger, more powerful, more organised waves at the beach than short-period swells of the same height.

Short-period swells, often called wind swell, are generated by local winds and tend to produce weaker, choppier, less organised waves. Long-period groundswell produces cleaner lines and more powerful waves, and it can make a modest swell height feel much bigger at exposed beaches and reefs.

Swell period: what it usually means at the beach
Period	Type of swell	Typical effect
Under 8 seconds	Wind swell	Weaker, choppier, less organised waves
8–11 seconds	Mixed swell	Moderate power and organisation
12 seconds and over	Groundswell	Cleaner lines, more power, bigger at exposed spots

Swell direction

Swell direction tells you where the swell is coming from, usually given as a compass direction or degrees. It matters because each beach or reef faces a particular direction and is exposed to swell from some directions but sheltered from others. A beach facing west will usually pick up a west swell well but may miss a south swell.

This is why places such as Peniche and Sagres, with beaches facing several directions, are so reliable: whatever the swell direction, at least one beach is likely to pick it up or offer shelter. Learning which directions suit your local spots is one of the most important parts of reading a forecast.

Wind: offshore, onshore and cross-shore

Wind can make or break a session. An offshore wind blows from the land towards the sea, holding up the face of the waves and making them clean and well shaped. An onshore wind blows from the sea towards the land, making waves crumbly and choppy. A cross-shore wind blows along the coast, which can be acceptable when light but messy when strong.

Wind speed matters as much as direction. Light winds or no wind, often called glassy conditions, are ideal. Strong offshore winds can make paddling into waves difficult. Many coasts have light winds in the early morning, with sea breezes building in the afternoon, which is why surfers often go out at dawn.

Tides

Tides raise and lower the sea level, changing the depth of water over sandbanks and reefs. Some spots work best at low tide, others at mid or high tide, and some only work for a short window. At high tide, some beaches become too deep and waves break close to the shore; at low tide, reefs can become dangerously shallow.

Tide tables give the times and heights of high and low tide. Local surfers, surf schools and guidebooks can tell you which tide suits each spot. Ask, watch and keep notes, and you will soon learn the patterns.

Putting it all together

The best session happens when the swell, wind and tide all line up for a particular spot. Start with the swell: is it the right size and direction for the beach you have in mind, with a period that suits your level? Then check the wind: is it offshore, light or onshore at that beach, and how will it change during the day? Finally, check the tide: does the spot work at the times you can surf?

When conditions are not right at one beach, look for another nearby that faces a different direction or works at a different tide. Always check the conditions in person before paddling out. Forecasts are models, not guarantees, and the ocean can surprise you.

Safety and when not to go

Reading a forecast is also about knowing when not to surf. Big swells, strong winds, storms and dangerous rip currents can make conditions unsafe, especially for beginners. Check official marine warnings from national weather services, follow lifeguard advice and choose conditions within your ability.

If you are unsure, watch for a while before paddling out, ask local surfers or a surf school, or simply wait for another day. Sitting out a session is part of good surfing.

Questions

What is a good swell period for surfing?

Longer periods, typically above about 10 to 12 seconds, usually mean more powerful, organised groundswell. Short periods often mean weaker, choppier wind swell. The best period depends on the spot and your level.

What does offshore wind mean?

An offshore wind blows from the land towards the sea. It grooms the waves, holding up their faces and making them clean. Onshore wind, blowing from the sea, makes waves choppy.

Is the swell height the size of the waves?

Not exactly. Swell height refers to the open-ocean swell. Breaking waves can be bigger or smaller depending on the beach's exposure, the seabed and the swell direction and period.

What tide is best for surfing?

It depends on the spot. Some beaches and reefs work best at low tide, others at mid or high tide. Ask local surfers or schools and learn the patterns of your local breaks.

Why are the waves smaller than the forecast?

Breaking waves depend on the beach's exposure to the swell direction, the shape of the seabed, the tide and the wind. A beach sheltered from the swell direction, or a high tide over a sandbank, can produce much smaller waves than the open-ocean forecast suggests.

When is the best time of day to surf?

Often early morning, when winds are lightest and conditions are cleanest. Many coasts develop onshore sea breezes in the afternoon. The best time also depends on the tide that suits your spot.

Which surf forecast should I trust?

Forecasts use computer models and can differ. Compare more than one source, check official marine warnings and real-time buoy data, and always look at the beach before paddling out.

Plan the trip

Sources

These are editorial planning suggestions, not a substitute for local instruction or current conditions. How we write our guides.