Sea breezes and land breezes
1The lesson in plain words
On a sunny day the land heats faster than the sea and draws in a sea breeze. At night the land cools and a weaker land breeze blows out.
How a sea breeze forms
The sun heats the land much faster than the sea. Air over the land warms and rises, and cooler air from the sea flows in to replace it. A weaker flow higher up returns air to sea. This onshore wind blows from sea to land. It is the sea breeze, called virazón in Spanish.
Its day
It usually starts in the late morning near the shore, spreads out to sea and inland, peaks in mid-afternoon and dies near sunset. It typically reaches 10–15 knots, and can exceed 20 knots on hot coasts. In the Northern Hemisphere its direction tends to veer, or turn clockwise, through the afternoon.
When it fails or grows
Strong daytime heating and a light gradient wind, the background wind from weather systems, favour a distinct sea breeze. Strong offshore flow, from land to sea, can keep the sea breeze offshore; around 15 knots is only a rough guide. Light offshore flow may leave a calm zone between opposing winds. A light onshore background wind can reinforce it; check whether the coastal forecast already includes this.
The land breeze
On a clear night the land cools faster than the sea. Air flows off the land: the land breeze, called terral in Spanish. It is usually weaker, often under 10 knots, and strongest near dawn. Off mountain valleys it combines with cold air sliding downhill and can be much stronger.
Using them
Leave early on a calm morning, before the sea breeze, or use it for a sail back in the afternoon. Expect choppy water and stronger wind off a sunny beach in the afternoon. At anchor, check that the bay is sheltered from both the afternoon sea breeze and the night land breeze.
2Key data
- Sea breeze (virazón)
- Onshore, by day; starts late morning, peaks mid-afternoon
- Typical sea breeze
- 10–15 knots; over 20 knots on hot coasts
- Offshore background wind
- Strong flow may prevent the sea breeze reaching the coast
- Land breeze (terral)
- Offshore, at night; usually under 10 knots, strongest at dawn
- Northern Hemisphere
- Sea breeze tends to veer during the afternoon
3Key points
- 1
Sea breeze: by day, from the sea, peaking mid-afternoon.
- 2
Land breeze: by night, off the land, usually lighter.
- 3
Strong daytime heating and light background winds favour a distinct sea breeze.
- 4
An onshore background wind can reinforce the sea breeze.
- 5
Check anchorages for both the afternoon and the night wind.
4Frequent mistakes
Wrong: A forecast of force 2 means a quiet afternoon on a sunny coast.
Right: A broad offshore forecast may miss a local sea breeze. Check the coastal forecast for afternoon strengthening rather than adding a fixed amount.
Wrong: The land breeze blows from the sea at night.
Right: The land breeze blows from the land towards the sea. The sea breeze blows from the sea by day.
5Practice case & exam keys
A sunny summer day on the Costa Brava. The forecast gives a light westerly, offshore, force 2. You plan to sail out at 1100 and return to the harbour at 1700. What wind should you expect? How could this affect your return?
Show the answer
Expect the light offshore wind first, then a possible onshore sea breeze building through the afternoon. Check the coastal forecast and whether your harbour entrance faces that wind. If the expected chop would make entry difficult, return earlier or choose a sheltered alternative.
Exam keys
- Sea breeze (virazón): daytime, sea to land, caused by the land heating faster than the sea.
- Land breeze (terral): night-time, land to sea, usually weaker.
- Strong offshore flow may keep the sea breeze from reaching the coast; onshore flow can strengthen it.
Finish this unit
When you've read it, match the terms, then answer three questions. Get them all right to finish the unit; opening the page alone doesn't count.
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