Spend a summer day at a coastal airfield and you will feel the wind swing onshore by the afternoon and then fall away and reverse overnight. That daily rhythm is the sea and land breeze, a local circulation driven by nothing more than the different way land and water respond to the sun. It is small in scale but real in its effect on a coastal aerodrome.
This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.
The cause: land and sea heat differently
The whole phenomenon comes from one fact: land heats and cools much faster than water. The sun warms a land surface quickly, and that surface warms the air above it; water, with its huge thermal inertia and its ability to mix and to let light penetrate, warms far more slowly and stays a more even temperature. At night the reverse holds: the land cools quickly while the sea holds its warmth. That difference in temperature between the air over the land and the air over the sea is the engine of the breeze, and because the sun drives it, the circulation runs on a daily (diurnal) cycle.
The sea breeze
By day, the land warms faster, so the air over the land becomes warm and rises. Rising air leaves slightly lower pressure near the surface over the land, and the cooler, denser air sitting over the sea flows in to fill the gap. That inflow, from sea to land, is the sea breeze: an onshore wind. It does not appear at dawn; it builds as the land heats through the morning, is usually strongest in the afternoon, and can reach tens of kilometres inland by late in the day. The air it brings is cooler and moister than the air it replaces, which is why a hot coastal afternoon can suddenly turn fresh when the sea breeze sets in.
The sea-breeze front
As the cool marine air pushes inland, it meets the warmer air over the land, and the boundary between them is the sea-breeze front. It behaves like a miniature cold front: the cool, dense sea air undercuts the warm inland air and lifts it, so the front is often marked by a wind shift, a line of cumulus cloud, and sometimes showers triggered by the lifting. Inland, the convergence along the front can be enough to set off convection on a warm, unstable day. For a pilot this matters because the front is a moving line where the wind, the cloud and the turbulence all change, and it can pass over an inland aerodrome during the afternoon.
The land breeze
At night, the cycle reverses. The land cools faster than the sea, so now the air over the warmer sea rises, and cooler air flows out from the land to replace it. That outflow, from land to sea, is the land breeze: an offshore wind, usually developing overnight and into the early morning. The land breeze is generally weaker than the sea breeze, because the night-time temperature difference between land and sea is smaller than the strong daytime contrast. It is the gentler, quieter half of the daily cycle, but it is real, and it explains why an offshore breeze often greets an early start at the coast.
What it means for a coastal aerodrome
The practical upshot for flying is that at a coastal aerodrome the wind can reverse between day and night, swinging onshore with the afternoon sea breeze and offshore with the overnight land breeze. That changes the runway in use and the crosswind through the day, so the crosswind component you plan for the morning may not be the one you meet in the afternoon. The sea breeze can also advect sea fog inland off a cold sea, bringing low visibility that our guide to fog, mist and the dewpoint spread explains, and the sea-breeze front can bring gusts, a wind shift on approach, and inland convection. None of this is dramatic individually, but together it makes a coastal aerodrome's weather notably time-of-day dependent.
When the sea breeze is strongest
The sea breeze is not the same strength every day, and a few conditions favour a vigorous one. A clear, sunny day heats the land hard and builds a big land-sea temperature contrast, the engine of the breeze, so the strongest sea breezes come on warm, sunny afternoons, often in spring and summer when the sea is still relatively cool. A light gradient wind, the broad-scale wind set by the pressure systems, lets the local breeze dominate; a strong gradient wind can overwhelm it or, depending on direction, either reinforce an onshore flow or hold the sea breeze offshore so it never comes in. So when you read a calm, sunny forecast at the coast, expect a sea breeze to build; when the gradient wind is strong, the local breeze may be masked.
A family of local winds
The sea and land breeze is one member of a larger family of thermally driven local winds that come from the same idea, surfaces heating and cooling at different rates. In hilly country, anabatic winds flow up sunlit slopes by day as the slope heats the air against it, and katabatic winds flow down slopes and valleys by night as the cooled, denser air drains downhill, often pooling cold air and fog in the valley floor. Like the sea breeze, these are gentle, predictable and tied to the time of day, and they matter at aerodromes set among hills or in valleys for the same reasons: a wind that changes with the sun. Recognising the sea breeze as one of this family makes the whole set easier to anticipate.
A worked example
You are planning two flights from a coastal airfield, one mid-morning and one late afternoon. At dawn there is a light offshore land breeze, the tail end of the night-time circulation. By mid-morning it has died away to near calm as the land warms and the system turns over.
By early afternoon the sea breeze has set in: a steady onshore wind, cooler and fresher, that has backed or veered the surface wind to blow in from the sea and freshened to a useful strength. The runway in use has changed to face it, and your crosswind for the afternoon flight is different from the morning's, so you re-check it. Inland, a line of cumulus marks the sea-breeze front advancing across the countryside, with a wind shift and a few showers along it that you note for the inland leg. By evening, as the land cools, the sea breeze fades and, overnight, the gentle land breeze returns. One airfield, one day, and the wind told the time.
Common pitfalls
- Assuming the morning wind holds all day. A sea breeze can set in by afternoon and change the runway and crosswind.
- Forgetting the front. The sea-breeze front brings a wind shift, cumulus and sometimes showers, and can trigger inland convection.
- Overlooking advected sea fog. A sea breeze off a cold sea can carry low visibility inland.
- Expecting a strong land breeze. It is the weaker half of the cycle, driven by a smaller night-time temperature difference.
- Treating it as only a coastal curiosity. The sea breeze can reach well inland and affect aerodromes some distance from the coast.
In Pilot EFB
Pilot EFB is a study and planning companion that helps you anticipate local effects like the sea breeze behind a forecast, alongside the decoded METAR, your crosswind notes and the rest of your briefing in one offline-first place. A briefing you have already pulled stays readable away from a signal, and pulling fresh weather needs a connection. Pilot EFB does not forecast the weather and is not a certified Electronic Flight Bag, so treat it as a study and planning aid and brief from your official source of record.