Sea Breeze

A sea breeze is a cool wind which develops near the coast on an otherwise calm, sunny, warm day. The breeze comes over the water and on to the land and usually is strongest in the mid-afternoon.

If it’s a perfectly still, sunny day and you’re thinking about having an evening BBQ, check your local forecast for mention of sea breezes as they might turn up uninvited. These winds are most common during the warmer months and because they are coming off the relatively cool water, they tend to bring a drop in temperature.

Sea breezes are most common around summer since that is when the land gets much hotter than the sea - it is this difference in temperature that creates the onshore wind. When the sun is high in the sky, the land heats up very quickly, the air near the surface is then warmed and this warm air begins to rise. The rising air creates an area for the cool air over the water to blow into – this wind will keep blowing until the surface begins to cool down. The breeze will ease from evening as the sun gets lower in the sky or significant cloud cover could reduce the surface warming.

You might be wondering why the air has to come from the sea? The answer has to do with temperature, density and air-pressure. As the air over the land warms, it becomes less dense and starts to rise. The rising air creates an area of low pressure at the surface. In contrast, the cooler air over the sea is denser and therefore represents an area of relatively high pressure. In nature, air will try to travel from areas of high pressure towards low pressure.

The rising air and surface wind actually set up a circulation where the rising air ends up traveling back offshore before being pulled down to sea level and blown back towards land.

Further points

Sea breezes will always be onshore winds but not all onshore winds will be sea breezes. A sea breeze will form on a calm, warm, sunny day but an onshore wind could be from a weather system generating a larger scale wind flow.

This type of wind is not just located near coastlines. A decent sized lake will also support the temperature difference and, therefore, pressure difference needed to generate the breeze; in this case it would be called a ‘lake breeze’.