TonnrHow to read a surf forecast: the basics
A forecast comes down to five figures: the height of the waves, their period, where the swell comes from, the wind and the tide. Five lessons, one demo each. Ten minutes before your first session.
On a spot's page, each underlined part of the sentence leads to its lesson:
Right now the waves are 1.4 m, with a period of 12 s, from WNW, the wind is 8 kn, from NE, Offshore, and the tide is rising, high water at 02:10 PM.
Height
The height announced is that of the swell out at sea: trough to crest, measured by a buoy or computed by a model. It is not the height of the wave you will see at the beach.
At the shore, the wave stands up as it touches the bottom, and it is often taller than the swell announced: 1 m out at sea can give 1.5 m on a reef, and less on a beach that spreads it out. Between the two, the period and the bottom make all the difference.
To start, look for 0.5 m to 1 m announced. Above 1.5 m, you spend the session paddling.
Slide: the color is the one the map gives that sea, and the wave is drawn against a surfer of 1.8 m.
Remember: The color of the sea on the map is that height.
Period
The period is the time between two waves, in seconds. It is the figure beginners skip, and the one that says the most.
A 14 s swell has crossed the ocean: long, orderly, powerful, it grows as it reaches the shore. An 8 s swell was born close by, in the wind: short, messy, it breaks any old way. At the same height, a 14 s wave carries almost twice the energy of an 8 s one, and looks bigger.
Under 8 s, it is chop. From 8 to 11 s, it can be surfed. Above 12 s, it is a real swell: exposed spots get big, sheltered spots wake up.
Same height. Slide from 8 to 14 s: the waves spread out, and the energy doubles.
Remember: At the same height, look at the period first.
Where the swell comes from
The direction is where the swell comes from, as for the wind: a west swell comes from the west. Tonnr writes it with an arrow that points the way it goes, then the name of the point it comes from.
A spot only receives the swell that enters its window: the part of the horizon it sees from the beach. A beach that faces west takes swells from the south-west to the north-west. A north swell passes offshore and leaves the beach flat, while the buoy says 2 m.
On a spot's page, the window is drawn as a ring. When the sea's sentence speaks of "the swell's direction", this is what it means: does today's swell enter the window.
Turn the swell in front of a beach that faces west. The ring is its window, drawn as on a spot's page.
Remember: 2 m at the buoy does nothing for a spot that cannot see it.
Wind
The wind is named from the beach. Offshore: it comes from the land and blows out to sea. It smooths the wave, holds it up, hollows it. Onshore: it comes from the sea. It makes the wave break too early, soft and messy. Cross-shore: it runs along the beach, and gets in the way without ruining everything.
The same wind is offshore here and onshore on the next beach, which faces another way. That is why Tonnr names it spot by spot.
Strength counts as much: up to 10 kn, almost anything goes. Beyond 20 kn, even offshore, it holds you at the top of the wave on the take-off.
Turn the wind in front of the same beach, then strengthen it: the wave smooths out or gets chopped up.
Remember: At dawn, the wind is often asleep. That is why sessions happen early.
Tide
The tide changes the depth of water over the bottom, and so how the wave breaks. At low tide, the bottom is close: the wave breaks fast, hollow, sometimes too much. At high tide, there is too much water: it breaks softly, or not at all. In between, at mid-tide, is the moment of most beaches.
Every spot has its own tide. Some only work at low tide, others only wake up at high tide. A spot's page says so when it is known, and the sea's sentence tells you whether the tide right now suits it.
Rising or falling counts too: the rising tide pushes the swell towards the beach and often makes things better; the falling tide empties the spot.
Run through the day: the water rises over the bottom of the spot.
Remember: Look at the time of high water before you look at the height.
You can read the sentence now.
Find your spot, read what the sea is doing there right now, and once you know what it likes, Tonnr tells you.
Next guide: Intermediate · Reading a week of forecasts and finding the right window