TROPICAL STORMS OVER TENERIFE

Tropical storms over Tenerife and the Canary archipelago are rather rare, although they are born with the regularity of a meteorological clock and develop extremely quickly over the Atlantic Ocean.

They travel back and forth, sometimes appearing deceptively out of nowhere. Do these tropical monsters ever reach Tenerife? No, the Canary Archipelago lies in a remote corner where hurricanes do not typically head. Or do they…?

Birth

During the autumn months, pressure systems cross the warm waters of the Atlantic Ocean. These systems thrive best when the sea temperature reaches 27 degrees Celsius or higher. Often, they begin forming over central Africa in an early stage as a cluster of well-developed and organised rain and thunderstorm systems. Once a clear circulation becomes visible (rotating counterclockwise), the first stage of a tropical hurricane is formed: the tropical depression. At this point, there is not yet much wind—at most, wind speeds of force 6 to 7 at sea and strong gusts accompanying the occasional heavy showers that can affect countries like Ivory Coast, Liberia, and Sierra Leone.

Route

From there, the depression is carried by upper atmospheric currents over the ocean, often passing south of the Cape Verde Islands, moving west-northwest. Along the way, the air mass absorbs a great deal of moisture and heat, and the strength increases due to the Earth’s rotation. This Coriolis force largely determines the circulation of air masses around all pressure systems. This is the reason why tropical depressions, storms, and hurricanes cannot form near the equator.

Development

As the depression develops further, this can be observed clearly on satellite images. A distinct spiral pattern in the cloud formations becomes increasingly evident. When wind speeds increase to force 8 or higher (34 knots or more than 63 km/h), the storm reaches the status of a tropical storm. At this moment, the storm receives a male or female name from a pre-determined list, which is reused every six years unless certain storms or hurricanes have made history.

A tropical hurricane is classified according to a category on the Saffir-Simpson scale, which has 5 categories: 1 being the weakest, and 5 the highest intensity.

Wind and Precipitation

Strong winds and moderate to heavy rainfall characterise intense tropical hurricanes, but they also bring what is known as a storm surge: a rise in water level caused by wind and low atmospheric pressure. This can result in waves between 4 and 6 metres high, which, when combined with an astronomical high tide, can swell into towering waves of more than 8 metres. The highest wind speeds occur near the hurricane’s eye, on the leeward side relative to the storm’s movement—often on the north to northwest side.

Delta in 2005

As a hurricane approaches, high, thin cloud cover increases to form a uniform, milky-white sky, which a few hours later turns into a grey gloom that releases the first rainfall. Closer to the eye, the wind intensifies dramatically, as does the rainfall, which can become highly convective. Within 24 hours, rainfall amounts can range from 100 to more than 300 mm (the equivalent of 10 to 30 buckets of water per square metre!). Wilma set the record in 2005 with a pressure drop to 900 hPa (hectopascal).

Looking back through the extensive database of the NHC (National Hurricane Center), which monitors all tropical systems worldwide, it has happened only twice since 1970 that a tropical storm approached the Canary Islands. The most intense was Delta, which left a trail of devastation over the islands between 22 and 30 November 2005.

In 2010, Otto passed by on 17 and 18 October, but it was nearly dissipated and moved north, dying out completely west of Morocco. Tropical storms over Tenerife are exceptional but not unheard of.

Should We Worry?

There is no need to worry about these tropical storms—unless they pass through our backyard. However, considering climate change and warming ocean waters, we might experience more extreme weather in the future.

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Tropical Storms Over Tenerife ©