Local weather: sea breezes, fog and coastal winds

On a sunny day the sun warms the ground and the sea at the same rate. What differs is where the heat stays: on land it stays in a thin top layer, so the air above the land gets much warmer; at sea it is spread down through the water.

The warm air over the land rises. Cooler, denser air from the sea flows in underneath to take its place, and higher up the air flows back out to sea, where it sinks: a circuit.

The sea breeze is the lower half of that circuit, blowing from the sea onto the land.

Where the sea air meets the land air there is a sharp boundary: the sea breeze front.

It usually blows on relatively calm, sunny days, above all in summer.

The day of a breeze

A sea breeze starts once the sun has warmed the land. It is usually strongest in the mid-afternoon, and eases from the evening as the sun gets lower in the sky; sooner if the sky clouds over.