Guide: reading the sea and the weather
A practical guide to understanding what MareCalmo's numbers mean so you can choose where to go with confidence. No needless jargon: just what you need to avoid picking the wrong day.
Watch the guided tour again A 30-second walkthrough of the map, filters and beach cardHow rough the sea is: the 5 states
To tell you what the sea is like in a simple way, we use five states, based on the wave height close to shore. It's the foundation of everything: almost every beach activity needs a low sea.
| State | Wave height | Colour |
|---|---|---|
| Flat ⭐ | up to 0.15 m (like a mirror) | green |
| Calm | 0.15–0.30 m (small waves) | green |
| Some waves | 0.30–0.60 m | yellow |
| Rough | 0.60–1.25 m | red |
| Very rough | over 1.25 m | red |
In practice, for a relaxed swim look for a Flat or Calm sea (green): the star ⭐ marks Flat, the very best condition. With Some waves (yellow) you can still go in with a little care; from Rough upwards (red) the waves make themselves felt and many activities become uncomfortable or inadvisable.
Wind waves and swell
Not all waves are the same. MareCalmo distinguishes two types, because they matter in different ways:
Wind waves (local sea)
Generated by the wind blowing right there at that moment. They are short, chaotic and vanish quickly when the wind drops. They are the ones that make swimming unpleasant on a windy day.
Swell / long sea
"Real" waves, generated by a distant storm, that travel for kilometres and arrive well spaced out and regular. They happen rarely: they are the ones you need for surfing, but they stir up the sand and reduce visibility for snorkelling.
The wind
The wind matters almost as much as the waves. We show the average speed and gusts in km/h, plus the direction. A few useful reference points:
- Below 12–15 km/h: light air, ideal for relaxing, SUP and canoeing.
- 15–25 km/h: breezy; your towel takes off and the sea gets choppy.
- Over 20–25 km/h with gusts: great for windsurfing and kiting, awkward for almost everything else.
It also matters a lot where it blows from: the same wind can leave one coast flat and make the opposite one unusable. That's why MareCalmo takes into account the exposure of each beach.
UV index, rain and water temperature
- UV index: measures the intensity of the sun's rays. In summer it easily reaches very high values (8–10): in the middle of the day you need shade and protection.
- Chance of rain: below 30% the day is considered reliable for spending time on the beach.
- Water temperature: from about 20 °C upwards swimming is comfortable for most people.
Choosing the right activity
MareCalmo doesn't just give you the raw numbers: for each activity it applies specific criteria and ranks the spots accordingly. Here's what each activity looks for.
Swimming
A relaxed swim: a Flat or Calm sea, water at least mild (≥ 20 °C) and light wind (below 25 km/h).
Relaxing
Sun umbrella and a nap: a calm sea, light wind (below 15 km/h) so your towel stays where it is, and a rain risk below 30%.
Snorkelling
To see well underwater you need a smooth surface: a calm sea, little wind (below 18 km/h) and no swell to stir up the sand.
SUP
Standing on the board you act like a sail: you need water like a mirror (a Flat sea), very little wind (below 12 km/h), low gusts and no thunderstorms.
Canoe / kayak
Sitting down you can tolerate a bit more: a flat sea, light wind (below 15 km/h), modest gusts and no thunderstorms.
Boating
A trip out on a pleasure boat: a manageable sea (up to Some waves, roughly within half a metre), wind below 25 km/h, no strong gusts and - a safety requirement - no thunderstorms.
Surfing
You need real waves from a distant storm (swell), at least half a metre high and well spaced out. It happens rarely: when it does, it's worth it.
Wind (windsurf / kite)
Here the wind is a plus: you need sustained air of at least 20 km/h with useful gusts over 25, and no thunderstorms.
Safety: three rules that always apply
- Forecasts are at the level of a stretch of coast (about 5 km): they give the trend, not certainty metre by metre.
- Watch out for currents and undertow, which you can't see in the numbers.
- Always respect the Harbour Master's Office orders and the bathing flags.