Seasons & Weather
The Sea Breeze Has a Timetable and It Is Daily
On calm sunny days a coastal wind builds through the morning, peaks in the afternoon and dies at evening, driven by land heating faster than water.
On many coasts a wind arrives off the sea in the late morning, strengthens all afternoon and disappears at dusk. It is generated locally and it runs on a schedule.
Land and water heat at different rates
Sunlight warms a thin surface layer of land quickly, while the same energy is mixed through a considerable depth of water and barely raises its temperature.
By mid-morning the air over the land is warmer, less dense and rising, which lowers pressure slightly at the surface compared with the air over the sea.
Air flows in to replace it, and that inflow is the sea breeze. It is a circulation, with a return flow aloft that is not felt at ground level.
The strength depends on the contrast
A clear, hot day over land with a cold sea produces the strongest breeze, which is why the effect is pronounced on coasts with cool offshore currents.
Cloud cover suppresses it by preventing the land from heating, and a strong prevailing wind overwhelms it entirely, either reinforcing or cancelling the local flow.
This is why a sea breeze can be a light air on one day and genuinely strong on the next without any change in the wider weather pattern.
It arrives as a front you can see
The leading edge of the breeze moves inland during the day, often marked by a line of small cloud where the cooler air lifts the warmer air ahead of it.
Its passage is noticeable: temperature drops, humidity rises and the wind swings, sometimes within a few minutes.
Inland penetration can reach a considerable distance by evening, which is why places well back from the coast can feel a sea breeze in the late afternoon.
The reverse runs at night
After sunset the land cools faster than the sea, reversing the temperature contrast, and a weaker flow runs from land to water.
This land breeze is usually lighter, because the night-time contrast is smaller, and it is most noticeable in the hours before dawn.
It is why the calmest water of the day often occurs early, before the sea breeze has begun and after the land breeze has faded.
Planning a day around it
Anything that wants flat water benefits from the morning, while anything that wants wind benefits from waiting until the afternoon.
Beach umbrellas, awnings and light gear that were fine at midday become a problem by three, and the strengthening is gradual enough that people miss it.
An offshore-blowing land breeze in the early morning carries inflatables and small craft away from the beach quietly, and that is when it is least expected.
Questions readers ask
Why is the coast windier than the forecast says?
Land forecasts are produced for typical inland exposure, and models smooth out coastal terrain. An open shoreline, a headland or a cliff top routinely experiences considerably more wind than the grid square value.
Which forecast should I use for a beach day?
The inshore waters forecast for the relevant stretch, together with a wave model and a local tide table. The general land forecast tells you about temperature and rain, and very little about what the sea will be doing.
