Land and sea disagree
Why Is It Windy at the Beach?
Land heats faster than sea, and the air rearranges itself all afternoon to fix it.
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Step 1 of 5
The same sunshine does different things.
Sunlight sinks metres into water and gets stirred through it. On land it only heats the top few millimetres, so land gets hot far faster.
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Step 2 of 5
Hot ground makes air above it rise.
Warm air spreads out and gets lighter than the air around it, so it floats upward, leaving slightly less air pressing down at the surface.
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Step 3 of 5
Air over the sea is heavier and slides in.
Cooler sea air presses down harder. Air always moves from harder-pressing to softer-pressing, so it flows in across the beach as a breeze.
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Step 4 of 5
The loop closes overhead.
The risen air spreads out high up, drifts back over the water and sinks. Land, sky, sea and back again — a slow wheel turning all afternoon.
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Step 5 of 5
At night it runs backwards.
The land cools quickly after sunset while the sea holds its heat, so the sea becomes the warm side and the breeze blows out from the land instead.
Sea breezes usually start a couple of hours after sunrise and reach thirty kilometres inland by evening.
The short version
Land heats faster than sea, so air rises over the land and cooler sea air slides in to replace it.
Try it yourself
On a still sunny day at a lake, note the wind at ten in the morning and again at three. It usually turns to face the water.
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