9 Surf Forecast Numbers That Separate a Good Session From a Great One

The most important number in any surf forecast is swell period. Around 13 seconds or longer means clean, powerful groundswell; below about 10 seconds you're usually looking at weak, disorganized windswell. But period is one of nine numbers that decide your session. Here's each one, and the exact figure to look for.

Most surfers read the wave height, maybe glance at the wind, and stop there. The ones who always seem to score read the whole picture. Every number below feeds directly into the Strike Score, and once you know the thresholds you can call a session before you've left the driveway.

1. Swell Period: look for 13 seconds or more

Period is the gap in seconds between one wave and the next. Under 10 seconds is windswell: short, weak, and choppy. From 13 to 16 seconds you have quality groundswell. Above 17 seconds you're into long-period energy that breaks with real power and pushes straight through surface chop. If you only check one number, check this one.

2. Swell Height: 3 to 6 feet suits most breaks

At the average beach or reef break, 3 to 6 feet of clean swell is the money zone. It's enough size to be fun without closing out. A big-wave spot wants 15 feet and up, and a mellow point can be perfect at 2. Height on its own tells you almost nothing until you pair it with period, which is why a "6 foot" forecast can mean a dream day or a mushy mess.

3. Wind Speed: keep it under 15 knots

Wind is what separates glassy from garbage. A light offshore breeze of 5 to 15 knots grooms the wave face and holds the lip up. Past 20 knots, even offshore wind starts to bump the surface and blow you off the back of the wave. Onshore wind ruins a wave at almost any speed.

4. Wind Direction: offshore beats onshore, every time

The wind you want blows from the land out to sea. That offshore flow cleans up the surface and steepens the face. Onshore wind, blowing from the sea onto the land, crumbles waves into mush. What counts is the angle relative to your break, so a light cross-offshore at around 10 knots is often the sweet spot. Every break has its own limit too: a sheltered slab falls apart above 25 km/h of wind, while an open beach break can hold together up to about 40.

5. Swell Direction: within about 30 degrees of the break's window

Every break has an ideal swell window. A south-facing beach wants south swell. Energy arriving more than 30 degrees off that optimum loses power and often refracts poorly on the way in. This is why two spots five minutes apart can score completely differently on the same day, and why a famous wave can sit flat while the beach around the corner fires.

6. Tide: know your spot's 2-to-4-hour window

Plenty of reefs and points only work in a narrow tidal band, often a two to four hour window around mid or low tide. Nail the size, period, and wind but surf the wrong tide, and the wave either backs right off or slams shut on the sand. This is the number local knowledge exists to solve, and where historical data earns its keep.

7. Water Temperature: below 18°C, bring the right rubber

Water temp doesn't change the wave, but it decides how long you last in it. Above 22°C you're in boardshorts or a springsuit. Between 18 and 22°C, reach for a 3/2. Below 12°C you want a 5/4 with boots and probably a hood. Getting the rubber wrong is the fastest way to cut a good session short.

8. Swell Consistency: a set every 60 to 120 seconds

A forecast can promise good size and still disappoint if the sets arrive in long, flat lulls. A rhythm of roughly one set every 60 to 120 seconds keeps you catching waves instead of bobbing around waiting. Two or more swells in the water at once usually tightens that rhythm up.

9. The Strike Score: 80 or higher means go

We fold all eight numbers above into a single figure from 0 to 100. A Strike Score of 80 or higher lands in the "Firing" band, which means the ingredients have lined up: long period, right direction, light offshore wind, cooperative tide. It's the quickest way to know whether today is worth the paddle without reading six variables yourself.

The Takeaway

Wave height alone is close to useless. Period, wind, direction, and tide are what turn a raw forecast into a decision. Learn these nine numbers and you'll stop guessing, or let the score do the arithmetic and just check where it's firing right now.

FAQ

What is the most important number in a surf forecast?

Swell period. Thirteen seconds or longer points to clean, powerful groundswell, while anything under about ten seconds is usually weak windswell.

What swell period is considered good for surfing?

Thirteen to sixteen seconds is quality groundswell, and seventeen seconds or more delivers long-period energy that breaks with real power.

What wind speed is best for surfing?

Offshore wind between 5 and 15 knots is ideal. Past roughly 20 knots, even offshore wind starts to degrade the wave face.

What does a Strike Score of 80 mean?

It lands in the Firing band, which means swell size, period, direction, wind, and tide have all lined up. A session worth rearranging your day for.