How BeachSea reads the sea

BeachSea stays quiet on an ordinary day, so when a card does appear it is worth knowing what it is telling you. Here is what each warning means and where it comes from.

The one it exists for: offshore wind

Wind blowing from the beach out to sea is the warning BeachSea was built around, and it is dangerous precisely when it does not look it.

Offshore wind flattens the water near the shore, so the sea looks inviting, while it pushes anything that floats away from land. Inflatables, boards and tired swimmers get carried out faster than they can swim back. A calm looking sea with the wind at your back is the classic set-up for a rescue.

This is why the sea direction step matters. Without it BeachSea knows the wind direction but not which way your beach faces, so it cannot tell offshore from onshore, and it says nothing rather than guess.

Rip currents: risk, never location

When conditions favour rips, BeachSea says so and opens an explainer. What it will never do is point at a spot and call it a rip.

No app can. Rips form from sandbars that shift with every tide and storm, and there is no live feed of rip positions anywhere in the world. Any app claiming to show you where one is, is guessing.

What the explainer teaches instead is worth more: how to read the water from the beach before you swim, and what to do if one catches you.

• Spot it. A gap in the breaking waves, a darker or calmer channel, foam and sand streaming out to sea.
• Swim parallel. Stay calm and float. Swim along the beach, not against the current, until you are out of the pull.
• Ride back in and signal. Once free, use the breaking waves to help you back to shore. Wave and call for help if you tire.

Water cleanliness after heavy rain

Rain in the last couple of days brings runoff and sewer overflow into the sea, which is why health authorities everywhere suggest waiting about a day before swimming, particularly near storm drains and river mouths. When that has happened at your beach, BeachSea mentions it.

At European beaches it also carries the official bathing water rating, but only when that rating is Poor or Sufficient. A beach rated Good or Excellent shows nothing, because a card that appears every time tells you nothing.

More than one thing can be true at once, and the cards stack when they are. Below, the sea is building, a rip is favoured, and the water is carrying runoff, so all three say so while the tiles underneath carry on reporting the numbers.

Cold water, and swell that is turning

Two quieter warnings round it out. Water cold enough to cut a swim short is flagged against the temperature rather than left as a number to interpret, and a swell that is building through the day shows as an advisory before it arrives, not after.

Everything above is guidance, not a guarantee. Conditions change faster than any forecast and no app can see the water in front of you, so obey the posted flags, swim near lifeguards, and when in doubt, stay out.