Leste

Madeirans give the name leste (hot, dry easterly wind from Africa) to the wind that blows from the direction of the African coast. It is always accompanied by a considerable rise in temperature and a high degree of atmospheric dryness. When it makes itself felt, the sun is dimmed and the sky is completely free of clouds, which seldom happens at other times. The leste generally begins as a hot breeze, followed by a strong wind, also hot, which raises clouds of dust on land and churns up the sea. Although it resembles the sirocco, which blows in the Mediterranean region, it is, unlike the sirocco, a dry wind. This is because it travels at a great height and cannot take up moisture from the wide expanse of sea it crosses. Birds and insects are sometimes carried by the leste as far as Madeira, and on many occasions a certain amount of dust and fine, impalpable sand, perhaps from the Sahara, has been seen settling on furniture. When these particles are suspended in it, the atmosphere looks as dense as if a mist were darkening it. James Yate Johnson says that on one occasion he found in this dust six diatoms and various fragments of others, all belonging to species that live in many countries of the world.

In 1750 Dr Heberden saw the thermometer in the shade register 22.7°, 24.4° and 25° during a leste, which is nothing out of the ordinary. Dr Heineken, who made observations on this island from 1824 to 1826, never saw the thermometer rise above 29.4° during the leste, although he knew that with this wind it had sometimes risen to 35° in the shade and 54.4° in the sun. In 1835 Dr Mason saw the thermometer rise during a leste to 27.2° in the shade and 58.8° in the sun, while the highest shade temperature observed by Roberto White, also during the leste, was 25°, on 23 February 1850. In more recent times, the highest shade temperatures recorded with the wind from the African coast were 32.5° (July 1882), 33.5° and 35.6° (August 1902), 37.3° (August 1907), 35.0° (July 1917), 37.0°, 37.2° and 38.4° (August 1919) and 34.0° (August 1920). On 3 December 1920, a day on which the east wind blew, the maximum shade temperature was 26.6° and the minimum 14.9°.

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Mac Euen’, says Dr Barral, ‘found on 17 February 1849, during the leste, a difference of 21° between the dry and the wet thermometer, which gives a relative humidity of 18 per cent in the atmosphere; and Baron von Humboldt speaks of 16 per cent as the smallest quantity of vapour and the greatest dryness observed in the lowest regions of the atmosphere, and this over a vast continent.

Although the degree of dryness recorded by Mac Euen is very rare, the difference between normal relative humidity and that observed when the leste blows is truly extraordinary. Some people are unaffected by the atmospheric conditions this wind brings, and even show greater activity and physical vigour when they occur. In others, however, the same conditions cause serious discomfort, though it never leads to fatal results.

When the leste blows, furniture dries out and sometimes cracks as if it had been exposed to fire, and plants wilt and lose all their sheen and freshness. Animals, and birds in particular, seem to suffer from this wind, which some have compared to the samiel, the simoom, the harmattan and other very hot, dry winds felt in the interior of the African regions.

Although the wind we are referring to comes from the ESE, in Funchal it always blows from the E. This seems to be because it bends or is deflected after striking the mountains. When the leste is weak, it is felt only in the high region of the island, which is always the part it strikes directly. The effects of this wind are barely noticeable in the inland valleys and on the north coast, even when it is blowing violently in the low southern region. There are occasions when a north wind blows at Ponta de São Lourenço while the leste blows in the city and other places. This proves that the wind is not always general, even though, when it blows in the low region, it is always felt in the high region of the island, at least up to 1,400 metres.

The leste lasts 1 to 5 days, rarely longer, and is usually followed by rain. In some years it does not appear at all, and in others it appears more than once. When it blows in winter, it loses some of its unpleasant character, and the islanders notice it only through the great dryness it causes in the atmosphere.

As to the places the leste strikes on reaching Madeira and the direction it takes afterwards, there are many obscure points that it would be in the interest of science to clarify. This can only be achieved, however, when meteorological stations are set up in the mountains and at the eastern tip of the island, and placed under the direction of capable men who are diligent in carrying out their duties. At the foot of the Pico de Teide, on Tenerife, there has been a meteorological observatory since 1908 which has rendered science many services, whereas here not a single step is taken to make proper use of a station built in 1895 near the Pico do Areeiro (‘sand-pit peak’), which was never provided with the staff and instruments needed for observations!

During the leste that struck Funchal from 21 to 27 August 1919, the wind was at first not felt beyond Ponta da Oliveira (‘olive-tree point’). When a violent fire broke out in the pine woods of Monte and São Roque, we observed that the smoke, judging by the direction it took, seemed to be driven by a NE wind. That leste was especially noteworthy for its duration and for the enormous damage it did to crops. It should also be noted that it was while it lasted that the highest shade temperature ever observed in Funchal since meteorological observations began here was recorded. Relative humidity fell to 28 per cent at 3 p.m. on 23 August, while at the same moment the thermometer in the sun read 57°. This temperature cannot be regarded as the maximum, since, as we said when discussing the climate, the sun’s greatest strength occurs not at that hour but much earlier. See Climate (1-273).