How to Read a Surf Forecast (Height, Period, Direction, Wind, Tide)

By Nick Peterson · Updated 2026-08-21 · ~9 min read

Answer: Read a surf forecast in this order: (1) swell period — 12s+ means real groundswell energy, under 9s is weak windswell; (2) swell height, remembering that 3ft at 14s usually beats 5ft at 8s; (3) swell direction — it must point at your break's exposure window; (4) wind — light or offshore is clean, onshore over ~12 knots ruins it; (5) tide — each break has a tide window, and the forecast only matters inside it. A day that passes all five is a go; one that fails wind or direction usually isn't, no matter how big the height number is.

Every surf forecast — Surfline, Windguru, Windy, a NOAA buoy page, or LazySurfer — is built from the same five ingredients. Once you can read them you can use any app, spot a forecast that's lying to you, and stop driving to flat or blown-out beaches. This guide walks through each number, what "good" looks like, and the order to check them in.

The five numbers, in the order that matters

Most beginners read height first. Most experienced surfers read period and wind first, because those decide whether the height number is worth anything.

Step 1: Swell period (seconds)

Period is the number of seconds between wave crests. It tells you how much energy is in the swell and how far it has travelled. It's the single most predictive number on the page.

Under 9s — local windswell. Weak, crumbly, close together. Surfable on a beach break; poor on reefs and points.
9–12s — mid-period. Decent push, works most spots, often the East Coast's best case.
12–16s — groundswell. Lined-up, powerful, wraps into points and bays.
16s+ — long-period groundswell from a distant storm. Much bigger on the beach than the height number suggests; sets are far apart.

On NOAA buoys this is DPD (dominant period). Read more: surf period explained and groundswell vs windswell.

Step 2: Swell height (feet or meters)

Height is how big the swell is in open water, not how big the wave will be on the beach. Two catches:

Height only means something with period. 3ft at 15s carries far more energy than 5ft at 7s and will produce bigger, better waves. Energy scales roughly with height squared times period.
Apps measure differently. Some report open-ocean swell height, some "surf height" or face height at the beach, and Hawaii uses its own scale. See Hawaiian vs face height.

On NOAA buoys this is WVHT (significant wave height — the average of the biggest third of waves, so individual sets run bigger).

Step 3: Swell direction (degrees or compass)

Direction is where the swell is coming from. 270° is from the west; 180° is from the south. Every break has an exposure window — a range of directions it can "see." A Southern California point that faces south-west lights up on 200–240° and can be flat on a 290° swell that's pumping 30 miles away.

Learn your break's window. Most spot pages list it; LazySurfer's spot pages show the directions logged sessions were rated highest on.
Long-period swells wrap further around headlands, widening the window a little.
Two swells at once (common) means the forecast may show a "primary" and "secondary" — check both.

On NOAA buoys this is MWD (mean wave direction). More: swell direction guide.

Step 4: Wind (speed and direction)

Wind is the number that turns a good forecast into a bad session. Offshore wind (blowing from land to sea) holds the face up and cleans it; onshore wind (sea to land) crumbles it. Rules of thumb:

Under ~5 knots from any direction: glassy, go.
Offshore up to ~15 knots: clean; above that it gets hard to paddle into.
Onshore over ~10–12 knots: blown out for most spots.
Sideshore: depends on the break; often rideable but bumpy.

Check wind at the time you'll surf, not the daily average — dawn is frequently offshore and afternoons onshore. See offshore vs onshore wind.

Step 5: Tide (height and direction)

Tide changes the depth of water over the sand or reef, and each break has a window where it works. Beach breaks often prefer low-to-mid incoming; reefs and points often want mid or higher. The forecast numbers above only count during your break's tide window. See best tide for surfing by break type.

Putting it together: a worked example

Forecast for a west-facing California beach break: 4.5ft @ 14s from 285°, wind 4 kt offshore at 7am rising to 12 kt onshore by noon, low tide 6:10am.

Period 14s: groundswell, real energy. Good.
Height 4.5ft at that period: chest-to-overhead faces at a beach break. Good (maybe big for a beginner).
Direction 285°: inside a west-facing window. Good.
Wind: offshore early, onshore by noon. Go early.
Tide: low at 6:10am, pushing through mid by 9. Beach break on a rising tide. Good.

Verdict: 7–9am. Same forecast with a 7s period or 15 kt onshore wind would be a no.

Common ways forecasts mislead you

Big height, short period. "6ft" at 7s is wind chop. Read the period.
Right size, wrong direction. The buoy shows 5ft but your break is shadowed from that angle.
Daily wind averages. A "10 kt" day can be glassy at dawn and blown out by 10am.
Model vs observation. A forecast is a prediction. A buoy is a measurement. When they disagree, the buoy is right about now. Learn to read one: how to read NOAA buoy data for surfing.
One rating for everyone. A "3-star" day on a generic rating can be a great longboard day or a terrible shortboard day. Your own history at the break is the best filter — which is the idea behind LazySurfer's personalized rating, trained on your logged sessions and live NOAA data. It's free; here's how it works.

Glossary: every term on this page

Surf period explained — seconds between waves and why it beats height.
Groundswell vs windswell — distant storm energy vs local slop.
Swell direction guide — compass bearings and how they line up with your coast.
Offshore vs onshore wind — the factor that decides clean from blown out.
Surf height: Hawaiian vs face — why "4ft" means different things.
Clean-up set — the bigger set that catches the lineup inside.
Best tide for surfing — by break type: beach, point, reef.

Frequently asked questions

What is the most important number in a surf forecast?

Swell period. It tells you how much energy the swell carries and how organized the waves will be. A long period (12 seconds or more) with modest height usually produces better surf than a big height with a short period. Wind is the second most important, because onshore wind can ruin an otherwise good forecast.

What does 3ft at 12 seconds mean?

It means the swell in open water is about 3 feet high with 12 seconds between wave crests. At 12 seconds that is a solid mid-to-long-period swell, so at an exposed beach it will typically produce waist-to-chest-high or bigger faces, depending on the break and tide.

Is a 10 second period good for surfing?

Ten seconds is a usable mid-period swell. It will produce decent waves at most beach breaks and many points, though it lacks the power and line-up of a 14-second groundswell. On the US East Coast, 10 seconds is often a good day.

How much wind is too much for surfing?

Onshore wind above roughly 10 to 12 knots blows out most spots. Offshore wind is fine up to about 15 knots; beyond that it becomes hard to paddle into waves. Under 5 knots from any direction is generally glassy.

What does swell direction mean in a surf forecast?

Swell direction is the compass bearing the swell is travelling from, in degrees: 270 is from the west, 180 from the south. Each break can only receive swell from a range of directions, so a swell outside that window produces little or no surf there.

Should I trust the forecast or the buoy?

For what is happening right now, trust the buoy: it is a measurement, not a prediction. Use the forecast to plan days ahead and the buoy reading to confirm on the morning.

Next: How to read NOAA buoy data for surfing · Best surf apps for beginners · All guides

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