The garbí: why the wind always gets up after lunch

Spend a few days on the Catalan or Valencian coast in summer and you will notice a rhythm. The morning sea is glassy. By two or three in the afternoon there is a breeze off the water, by five the umbrellas are struggling and the sea has gone from flat to a short, restless chop. By sunset it has dropped away again.

That wind is the garbí, and this app is named after it.

A name from the old wind rose

Before compass bearings, Mediterranean sailors named the eight winds by where they came from. In Catalan that rose runs tramuntana from the north, gregal from the north-east, llevant from the east, xaloc from the south-east, migjorn from the south, garbí from the south-west, ponent from the west and mestral from the north-west.

Garbí comes from the Arabic gharbī, meaning western — a reminder of how many Mediterranean wind names travelled across the sea along with everything else. On parts of the Valencian and Balearic coast the same south-westerly is called the llebeig, and you will hear both names used for what is essentially the same afternoon breeze.

What actually causes it

A sea breeze is a heat engine, and it runs on the difference between how land and water absorb the sun.

Land has little capacity to store heat, so a morning of sunshine warms it quickly. The sea, with an enormous capacity to store heat, barely changes. The air above the warm land expands and rises; air has to come in underneath to replace it, and the nearest available air is sitting over the cooler sea. That inflow is the breeze. It is not weather arriving from somewhere else — it is generated locally, by the beach you are standing on.

Its daily schedule

• Morning — little or no sea breeze. The land has not built enough of a temperature difference yet, and the sea is often at its calmest.
• Early afternoon — the breeze sets in, typically from the south-west on this coast.
• Mid to late afternoon — the strongest part of the day, and the choppiest water.
• Evening — the land cools, the engine stops, and the wind fades with the light.
• Overnight — sometimes the reverse: a light land breeze blowing offshore, which is part of why dawn so often finds the sea flat.

The timings shift with the season and the day, but the shape holds. If a forecast shows calm in the morning and 20 km/h in the afternoon on a settled sunny day, it is almost certainly describing a sea breeze rather than a weather system.

Why spring breezes can be the strongest

The engine runs on the temperature difference between land and sea, not on absolute heat. In late spring the land is heating rapidly while the sea is still holding onto winter, and that gap can be wider than it is in August, when the sea has caught up. This is why a May afternoon can produce a more insistent breeze than a July one, on a day that felt milder.

What it does to your afternoon

A sea breeze builds wind sea — short, steep, closely-spaced waves, quite different from the long swell that arrives from a distant storm. Wind sea is what makes swimming feel like work, gets water in your face, and makes it harder to keep an eye on children. It is also why the same wave height can feel completely different at ten in the morning and five in the afternoon.

Garbí treats anything up to about 10 km/h as calm and 35 km/h as thoroughly unpleasant, grading everything in between. Its best-day feature will not recommend a day forecast above 20 km/h, because a warm, flat, sunny day with a hard breeze across it is not the day you were hoping for.

How to use it

• Want flat water, for swimming, snorkelling or a paddle board? Go in the morning.
• Want wind, for sailing, windsurfing or a kite? The afternoon is reliable in a way that weather systems are not.
• Sitting on the beach all day? Take something that holds an umbrella down properly, and expect to need it after lunch.
• Checking the forecast the night before? Look at the hour you actually plan to swim, not the daily figure — on a sea-breeze day the daily average describes nobody's afternoon.

None of this is unique to Spain — sea breezes form on every sunlit coast. What is local is the name, the reliability, and the fact that an entire coastline has organised its afternoons around it for a very long time.