The Canary Current & the Climate

The Canary Islands sit at the same latitude as the Sahara, Florida and the Persian Gulf, and yet they never get properly hot — because a cold ocean current runs down past them and a steady north-east wind blows over the top of it. Those two things, working together every day of the year, are the entire explanation for the climate that brings a couple of million British and Irish visitors here annually.

The current is called the Canary Current, and it is the eastern edge of the great clockwise circulation of the North Atlantic. Water that has crossed to Europe in the Gulf Stream turns south off Portugal, cools on the way down, and slides past the islands towards the tropics before swinging west again. By the time it reaches the archipelago it is markedly colder than the latitude would suggest: broadly in the high teens Celsius at the winter low and the low-to-mid twenties at the late summer peak, where an unmodified subtropical sea would be several degrees warmer.

The wind is the alisio, the north-east trade wind, which blows across the islands for most of the year with a reliability that seems eerie if you are used to British weather. It picks up moisture and, crucially, coolness from that current on its way in. The result is an island group that hardly has seasons: a summer that rarely becomes oppressive, a winter that rarely stops being shirt-sleeve weather, and a sea that is swimmable all year without ever being bathwater.

Why a cold current sits off a hot coast

It is not only the journey south that cools the water. The trade winds blowing along the north-west African coast push surface water offshore, and because the Earth is rotating, the deflection pulls that surface layer away from the land. Water has to come from somewhere to replace it, so cold water rises from depth. This is upwelling, and the Canary Current system is one of the four great eastern-boundary upwelling regions in the world, alongside those off California, Peru and Namibia.

Deep water is cold and, more importantly, loaded with nutrients — the remains of everything that has sunk out of the sunlit layer for years. Bring it up into the light and you get an explosion of plankton, then of everything that eats plankton. The banks off the Saharan coast, a few hundred kilometres east of the islands, are among the richest fishing grounds in the Atlantic, and they are rich for exactly that reason.

The detail nobody tells you: clear water means poor water

Here is the thing worth carrying away, because it inverts the obvious assumption. The reason the sea around the Canaries is that startling deep blue, and the reason you can see thirty metres down on a good day at a dive site, is that the water immediately around the islands is relatively poor in plankton. The upwelling happens mainly against the African shelf; the islands sit out in deeper water beyond it. Clear water is empty water.

What productivity the islands do get comes from their own interference with the flow. Each island casts a wake, and the current shedding off its flanks spins up eddies — swirls tens of kilometres across that trail downstream for weeks, dragging deeper water upwards inside them. Those eddies act as floating nurseries, and they are a large part of why an archipelago in nutrient-poor water supports the marine life it does. Green Atlantic water full of life would be excellent for the fishermen and ruinous for the tourist brochures.

The sea of clouds

The wind does something equally important in the air. Cool, damp air sits in a layer perhaps a thousand to fifteen hundred metres deep over that cold current, and above it sits warm, dry air descending from the subtropical high. Warm air over cool air is stable — it will not mix — so the damp layer is capped, like a lid on a pan. Cloud forms at the top of it and can go no higher.

Push that layer against a mountain and it has to rise, which is when it delivers its moisture as drizzle and fog on the northern flanks. That is why the north sides of Tenerife, La Palma and Gran Canaria are green and terraced and the southern sides are the colour of a biscuit. It is why the laurel forests survive in a narrow altitude band and nowhere else. And it is why, driving up towards Teide, you climb through grey murk for twenty minutes and then burst out of the top of it into blazing sun with a white floor stretching to the horizon — the mar de nubes, the sea of clouds. The same inversion is what put the world's telescopes on the ridge above La Palma.

A spring climate, with two interruptions

The headline figures are famously flat: coastal daytime highs that sit somewhere in the low twenties in midwinter and the high twenties in late summer, with the north a couple of degrees cooler and cloudier than the south. Our fuller breakdown of how the islands' weather works month by month puts numbers to it.

Two things break the pattern. The first is the calima, when the wind swings round to the east and brings Saharan air — hot, dry and full of dust — straight across the islands. Temperatures can jump ten degrees in a day, the sky goes the colour of weak tea and Teide disappears. It usually lasts a few days. The second is the occasional autumn Atlantic low that ignores the trades entirely and dumps serious rain on the western islands.

What the wind means on the ground

The trade wind is a fact of daily life, not a weather event. It is why El Médano and the Fuerteventura coast host world-tour windsurfing and kitesurfing every summer, and why the same beaches can be less than relaxing for a sunbathe. It is why a north-coast terrace needs a windbreak and a south-coast one does not. Our answer to the windiness question goes island by island; the short form is that the wind is strongest in summer, strongest on the eastern islands and strongest in the afternoon.

Cold water, warm air, and what it does to swimming

The mismatch catches people out. On a 26-degree day in August the sea may be around 22 or 23, which is pleasant; on a 21-degree day in March it may be 18 or 19, which is brisk by Mediterranean standards and perfectly normal here. Within the archipelago the west and south are warmer than the north and east — El Hierro and the southern coasts get the mildest water, Lanzarote the coolest — and our page on sea temperatures through the year sets out the range. Plenty of residents swim all winter; plenty of visitors buy a shorty wetsuit and stop thinking about it.

Why every ship stopped here

The current and the wind together made the islands the most important junction in the Atlantic for four hundred years. A sailing ship leaving Europe for the Americas came south to the Canaries to pick up the trades, which blow steadily west from this latitude, and rode them across. Coming back, you sailed north to find the westerlies. That is why Columbus stopped here on every crossing, why the Spanish treasure fleets used the same route, and why the islands ended up being fought over by everybody with a navy. Geography did not make them rich by accident; it made them unavoidable.

The living dividend

Cool, clear, deep water close to shore is an unusual combination, and it produces the archipelago's best wildlife. The channel between Tenerife and La Gomera holds a resident population of short-finned pilot whales and bottlenose dolphins, one of the most reliable whale-watching grounds in Europe. Loggerhead turtles drift in on these same currents from the far side of the ocean and stay for years. And the fish that ends up on your plate — vieja, cherne, sama — comes out of the same system, which is why Canarian fish cookery is so plain: the raw material does not need help.

The bottom line

Two invisible forces do all the work here. A current that is too cold for the latitude keeps the summers civilised and the sea honest; a wind that never quite stops keeps the air moving, builds the cloud sea that greens the north, and carried every ship that mattered out of European history and into the Americas.

It is also, in the end, the commercial basis of the entire archipelago. Nobody would fly four hours in February for a place that was merely sunny — winter sun at this reliability exists because of a cold current, and the islands have been selling the consequences ever since.