Climate

     The main factors determining the climate of the Canary Islands are as follows:
    -The Azores High. The Azores High prevails over the Canary Islands around 90 per cent of the time during the summer, and 50 per cent of the time during the rest of the year. It produces very stable weather, with moderately warm temperatures, no rainfall, overcast skies on the north-facing slopes due to the sea of clouds effect, and clear skies on the south-facing slopes. Most characteristically, it produces a type of wind known as the trade winds, which blow across the Atlantic Ocean at a speed of around 20 km per hour and, as they travel, take on the coolness and humidity of the sea. This is why, when they reach the islands, they cool the air and moderate the temperatures.
    -North Atlantic storms. During the winter, the Azores High weakens, allowing storms from the North Atlantic to pass through, bringing cold and rainy weather.
    -Tropical storms. These are caused by the arrival of storms from the south and west. They are most common in winter, although in some years none occur at all. Temperatures drop slightly and rainfall becomes widespread, even on the southern slopes of the islands. On the highest peaks, such as Mount Teide or Roque de los Muchachos, they can lead to heavy snowfall.
    -‘Tiempo sur’. The phenomenon known in the Canary Islands as ‘tiempo sur’ originates from the nearby Sahara Desert, which, particularly in summer and to a lesser extent in winter and spring, brings dry, hot weather with abundant clouds of suspended dust (calima), and sometimes strong winds.
    -The Canary Current. The temperatures of the waters surrounding our archipelago are cooler than one would expect given their geographical location, due to the presence of the so-called Canary Current, which moderates temperatures and prevents hurricanes and tropical storms from reaching the islands.
     -The terrain. In the Canary Islands, temperatures drop by around one degree Celsius for every 100 metres of altitude gain, until they reach the thermal inversion zone of the trade winds, at an altitude of around 1,500 metres. Furthermore, when the lower, moisture-laden trade winds collide with the mountainous areas on the north-facing side of the islands, they cool and condense, forming what is known as a sea of clouds: a dense layer of clouds, flat on top and laden with moisture.

The trade winds

       The trade winds are winds that blow over the archipelago almost constantly, although they are stronger during the summer months and weaker and more intermittent in winter. Their most distinctive feature is their arrangement in two superimposed layers: a lower, humid layer blowing from the north-east, and an upper layer of dry, warm air blowing from the north-west. When these layers interact, they create a temperature inversion with variable boundaries, the most striking consequence of which is the formation of what is known as a sea of clouds. This phenomenon occurs when the air, upon colliding with the mountains, is forced to rise and cools almost to the point of condensation, giving rise to a dense cloud formation which, unable to develop upwards, spreads horizontally, covering large areas of the northern slopes of the highest islands.
    In turn, the presence of the sea of clouds gives rise to another phenomenon known as horizontal rain, which occurs when moisture from the clouds condenses on the leaves of trees, forming water droplets that eventually slide down the leaves and fall to the ground. And it is precisely these climatic conditions that allow for the existence of a type of forest that is almost non-existent in other parts of the world: the laurel forest, a remnant of the great temperate forests of the Tertiary Period that is found in only a handful of places on the planet.

Types of weather

     The different types of weather experienced in the Canary Islands depend primarily on the air masses affecting the archipelago at any given time. The most common is the tropical maritime air mass, which, due to its oceanic origin, has a high relative humidity. At its centre lies the Azores High, whose most characteristic feature is the atmospheric stability it creates and its resulting influence on the typical weather in the Canary Islands, with mild temperatures in winter and cool temperatures in summer, and moderate humidity throughout almost the whole year.
    When temperatures drop and the sky becomes overcast with dark, rain-bearing clouds, the archipelago comes under the influence of the polar maritime air mass, originating from the North Atlantic, which generates significant atmospheric instability, occasionally leading to heavy rain and snowfall, as well as very low temperatures. Finally, when temperatures on the islands rise and the air feels very dry, the Canary Islands are under the influence of a tropical continental air mass originating from the Sahara Desert, which generally brings with it a large amount of airborne dust known on our islands as ‘calima’ or ‘calina’; when at its densest, this can reduce visibility to just a few dozen metres.

Rainfall

      In mid-altitude areas, rainfall can reach 800–1,000 mm per year on north-facing slopes, which are exposed to constant, humid trade winds. It is in this sector that the sea of clouds stagnates, bringing high levels of atmospheric humidity and a considerable volume of water, making the area ideal for agriculture. In contrast, on the south-facing slopes, rainfall is significantly reduced as the sea of clouds dissipates.
    In the high-altitude areas, mainly on the highest islands, the trade winds cease to have an effect; rainfall averages around 400 mm per year, well below the levels seen in the mid-altitude regions, and in many cases falls as snow.

     Rainfall in the Canary Islands is heaviest in late autumn and, above all, in winter, with summer being the driest season of the year. Rainfall is characterised by inter-annual variability; in other words, there is a succession of rainy or very rainy years, alternating with dry or very dry years. Rainfall is usually very localised, and on some occasions it poses a significant weather risk. When there is a sharp descent of air masses from the temperate zone, combined with tropical factors, very intense rainfall can occur within a very short space of time, causing torrential downpours comparable to those caused by the ‘cold drop’ phenomenon that occurs in late summer in the Mediterranean basin.

Temperatures

     As far as temperatures are concerned, the archipelago is characterised by mild climatic conditions. Generally speaking, the warmest temperatures are recorded on the southern coasts of all the islands, where the annual average exceeds 20°C. On the islands of Lanzarote and Fuerteventura, which do not reach altitudes of 1,000 metres and are therefore below the level at which sea fog forms, this average temperature is found across almost their entire surface, making them the driest islands. On the other islands, as altitude increases, the average annual temperature drops to around 14°C on the peaks of Gran Canaria, to 13°C on those of El Hierro and La Gomera, to around 9°C in the highlands of La Palma, and to as low as 5°C in the Cañadas del Teide on Tenerife.