What a Surf Forecast Actually Tells You
A surf forecast is a prediction of ocean and atmospheric conditions at a specific location. Unlike a simple weather forecast that tells you it will be sunny or rainy, a surf forecast gives you a layered picture: how big the waves will be, how powerful they will feel, where they are coming from, and what the wind will do to them when they arrive.
Reading one well is the difference between driving an hour to find two-foot mush and showing up at the exact moment a solid swell peaks with glassy conditions. This guide walks through every number you will see on a forecast, what it means in the water, and how to combine them into a clear go/no-go decision.
Wave Height
Wave height is usually the first number you see on a forecast, and it is also the most misunderstood. Forecasts show significant wave height, abbreviated Hs — the average height of the highest one-third of waves measured by instruments out at sea.
Significant wave height is not the same as the face height you will surf. The relationship between forecast height and what you experience in the lineup varies by location, break type, and swell direction. As a rough rule of thumb:
- A beach break will typically produce faces roughly 1.5 to 2 times the significant wave height- A powerful reef break facing a long-period swell can double or even triple it
This is why you will sometimes see Groundswell's forecast say 1.5 m and arrive at a break with legitimate overhead surf. The instruments were right — the ocean and the reef did the rest.
Swell Period
If wave height tells you how much energy is in the ocean, swell period tells you the quality of that energy. Period is measured in seconds — specifically, the time between successive wave crests passing a fixed point.
Short-period swells (under 8 seconds) are usually locally generated wind chop. The waves are close together, disorganised, and tend to crumble rather than break cleanly.
Long-period swells (12 seconds and above) have typically travelled thousands of kilometres from distant storms. They carry far more energy per wave, stand up cleanly on shallow reefs, and produce the powerful, hollow surf most surfers are looking for.
A practical example: a 1.5 m swell at 7 seconds will produce inconsistent, mushy waves at most breaks. The same 1.5 m at 14 seconds will produce double-overhead faces at a proper reef, with heavy lips and long walls. The height is identical; the experience is completely different.
Swell Direction
Swell direction is where the waves are coming from, expressed as a compass bearing. A swell of 315° is coming from the northwest; a swell of 200° is coming from the south-southwest.
Direction matters because every break has an optimal swell window — the range of directions it is exposed to and angled correctly to produce its best surf. A break facing north will light up in a northwest swell and see nothing from a south swell. A point break that wraps around a headland might need a very specific direction to produce long walls.
When reading a forecast, always check whether the swell direction is within the optimal window for your break. A large swell hitting from the wrong angle will produce lumpy, shifting surf at best — or nothing at all.
Wind
Wind is the single biggest factor in surf quality on any given day. Even a perfect swell with ideal direction can be ruined by the wrong wind. There are three scenarios:
Offshore winds blow from the land toward the ocean. They groom the wave face, hold up the lip, and produce the glassy, hollow conditions shown in every surf photo. This is what you are hoping for.
Onshore winds blow from the ocean toward the land — the same direction the waves are travelling. They create surface chop, push the lip over prematurely, and turn waves into disorganised white water. Strong onshore winds make most breaks unsurfable regardless of swell size.
Cross-shore winds blow parallel to the beach. Their effect depends on the break and the angle. A light cross-shore is often acceptable; a strong one will affect consistency and make paddling difficult.
When reading a forecast, look at both wind direction and wind speed. Light offshore (under 15 km/h) is excellent. Strong offshore (over 30 km/h) can actually blow the tops off waves and make paddling out brutal. Ideal conditions are usually a light to moderate offshore — enough to groom the surface without overpowering the break.
Tides
Tides change the depth of water over a break, and depth determines how waves behave. A reef break that produces perfect barrels at low tide might be a flat, unsurfable wall at high tide. A beach break that closes out at low tide might produce punchy peaks at mid tide.
Most surf forecasts include a tide chart showing the predicted high and low tide times and heights throughout the day. Learning which tide your local breaks prefer takes time in the water — but once you know, you can use the tide chart to identify the two or three hours in each day when conditions will be best.
Putting It All Together
A complete forecast read takes thirty seconds once you know what to look for. Run through this checklist:
1. Is there enough swell? Check wave height and compare to what your break needs to break properly.
2. Is the period long enough? Under 8 seconds usually means weak, disorganised surf. Over 12 seconds means power.
3. Is the direction right? If the swell is outside your break's optimal window, size and period won't matter.
4. What is the wind doing? Offshore and light is the goal. Onshore means a difficult session regardless of everything else.
5. Where is the tide? Check whether your break is best at low, mid, or high tide and plan your session timing accordingly.
When all five boxes are checked, you have the makings of a great session. The forecast is a prediction — conditions can vary from what is shown, particularly close to shore — but understanding these fundamentals will make you a sharper reader of the ocean and a more consistent surfer.
Try It Now
Groundswell shows all of these variables in one place — wave height, swell period, direction, wind, and tides — updated hourly from open ocean data, for any surf spot on earth. Check today's forecast at groundswell.surf or browse the surf spot directory to see live conditions at over 400 of the world's best breaks.