How to read a surf report and forecast

A surf forecast is six numbers for each hour. Read them in this order and you know what the waves will do. Here is a real hour from the BarrelFare forecast, then each line explained.

Waves

3 ft faces

Period

12 s

Swell

from the SSW (196°)

Wind

7 kt from the ENE, offshore

Tide

1.2 m, rising

Score

5.1 of 10

1. Wave height

There are two heights. The buoy height is the swell out at sea, the average of the biggest third of the waves. The face height is the wave you ride, measured on its front as it breaks. BarrelFare shows face height in feet.

The same buoy height can make very different faces. The period decides how much.

2. Period

The seconds between two waves. A long period means a swell from a far, strong storm: bigger, stronger waves for the same buoy height. Under 9 seconds is wind swell; 13 and up is groundswell.

Lesson: wave period, with a calculator

3. Swell direction

The compass direction the swell comes from. Each break is open to some directions and blocked from the rest by the coastline. A big swell from the wrong direction can leave a break flat.

Lesson: swell direction and the swell window

4. Wind

Offshore wind blows from the land to the sea. It holds the wave face up and makes it clean. Onshore wind blows from the sea and breaks the waves up. Cross-shore is in between. Under about 4 knots, the water is glassy. Wind is often lightest early in the morning.

5. Tide

The water level changes through the day. Many reefs need mid or high tide to cover the reef. Some beaches close out at high tide and work best on a rising tide. Each BarrelFare spot page says which tide that break likes.

6. The score

BarrelFare puts the five numbers above into one score from 0 to 10 for each hour. It compares the face height to the size the break handles best, and checks the swell direction against the break's window, the wind against its offshore direction and the tide against its best tide. Red is poor, green is good.

In the example, Lower Trestles has about 3 ft faces on a 12-second swell with offshore wind. That reads as a fair session: rideable, not special, and the score says the same.

Lessons

• Wave period: what the seconds mean for surf
• Swell direction and the swell window
• Offshore and onshore wind: why surf is best early
• Tide and surf: why the same spot changes in three hours
• Surf seasons: why summer goes flat, and where it doesn't
• Buoy height vs wave face: why 4 ft can be over your head
• Beach, point and reef breaks: why the bottom shapes the wave
• El Niño and surf: why some winters never stop

Glossary: every surf term in one list