Western Mediterranean weather

The weather pattern in the basin of the western Mediterranean is affected by many different systems. It is largely unpredictable, quick to change and often very different at places only a short distance apart. See Appendix III for Spanish meteorological terms.

WINDS

Winds most frequently blow from the west, northwest, north and east but are considerably altered by the effects of local topography. The Mediterranean is an area of calms and gales and the old saying that in summer there are nine days of light winds followed by a gale is very close to reality. Close to the coast, normal sea and land breezes are experienced on calm days. Along the Costa Brava, northwest, north and northeast winds are most common, especially in winter, though winds from other directions frequently occur. This area is particularly influenced by the weather in the Golfo de León and is in the direct path of the northwesterly tramontana (see below), making it particularly important to listen to regular weather forecasts.

The winds in the Mediterranean have been given special names dependent on their direction and characteristics. Those that affect this coast are detailed below.

Northwest - tramontana

This wind, also known as the maestral near Rio Ebro and the mistral in France, is a strong, dry wind, cold in winter, which can be dangerous. It is caused by a secondary depression forming in the Golfo de León or the Golfo de Genova on the cold front of a major depression crossing France. The northwesterly airflow generated is compressed between the Alps and the Pyrenees and flows into the Mediterranean basin. In Spain it chiefly affects the coast to the north of Barcelona, the Islas Baleares, and is strongest at the northern end of the Costa Brava.

The tramontana can be dangerous in that it can arrive and reach gale force in as little as fifteen minutes on a calm sunny day with virtually no warning. Signs to watch for are brilliant visibility, clear sky - sometimes with cigar-shaped clouds - very dry air and a steady or slightly rising barometer. On rare occasions the sky may be cloudy when the wind first arrives although it clears later. Sometimes the barometer will plunge in normal fashion, rising quickly after the gale has passed. If at sea and some way from land, a line of white on the horizon and a developing swell give a few minutes' warning. The only effective warning that can be obtained is by radio - Marseille (in French) and Monaco (in French and English) are probably the best bet. See page 13 for transmission details.

The tramontana normally blows for at least three days but may last for a week or longer. It is frequent in the winter months, blowing for a third of the time and can reach F10 (50 knots) or more. In summer it is neither as strong nor as frequent.

West - vendaval

A depression crossing Spain or southern France creates a strong southwest to west wind, the vendaval or poniente, which funnels through the Strait of Gibraltar and along the south coast of Spain. Though normally confined to the south and southeast coasts, it occasionally blows in the northeast of the area. It is usually short-lived and at its strongest from late autumn to early spring.

East - levante

Encountered from Gibraltar to Valencia and beyond, the levante, sometimes called the llevantade when it blows at gale force, is caused by a depression located between the Islas Baleares and the North African coast. It is preceded by a heavy swell (las tascas), cold damp air, poor visibility and low cloud which forms first around the higher hills. Heavy and prolonged rainfall is .more likely in spring and autumn than summer. A levante may last for three or four days.

South - siroco

The hot wind from the south is created by a depression moving east along or just south of the North African coast. By the time this dry wind reaches Spain it can be very humid, with haze and cloud. If strong it carries dust, and should it rain when the cold front comes through, the water may be red or brown and the dust will set like cement. This wind is sometimes called the leveche in southeast Spain. It occurs most frequently in summer, seldom lasting more than one or two days.

Clouds

Cloud cover of between 4/8ths and 5/8ths in the winter months is about double the summer average of 2/8ths. Barcelona, however, seems to manage a year round average of 3/8th to 5/8ths. The cloud is normally cumulus and high level. In strong winds with a southerly component, complete cloud cover can be expected.

Precipitation

Annual rainfall is moderate and decreases towards the north from about 760mm at Gibraltar to 560mm at Barcelona. The rainy seasons predominantly in autumn and winter and in most areas the summer months are virtually dry. The Costa Brava however usually manages about 25mm of rain during each summer month. Most of the rain falls in very heavy showers of 1-2 hours.

Thunderstorms

Thunderstorms are most frequent in the autumn at up to four or five each month, and can be accompanied by hail.

Water spouts

Water spouts occur in the Strait of Gibraltar in winter and spring, usually associated with thunderstorms.

Snow

Snow at sea level is very rare but it falls and remains on the higher mountain ranges inland. Snow on the Sierra Nevada is particularly noticeable from the sea.

Visibility

Fog occurs about four days a month in summer along the Costa de Sol but elsewhere is very rare. Occasionally dust carried by the southerly siroco reduces visibility and industrial areas such as Valencia and Barcelona produce haze.

Temperature

Winter temperatures at Gibraltar average 10-15 °C, rising steadily after March to average 20-29 °C in July and August. Afternoon (maximum) temperatures may reach

30-33 °C in these months. At Barcelona, summer temperatures are much the same as at Gibraltar but winter temperatures are lower, 6-13°C.

Humidity

The relative humidity is moderate at around 60% to 80%. With winds from the west, northwest or north, low humidity can be expected; with winds off the sea, high humidity is normal. The relative humidity increases throughout the night and falls by day.

Local variations

In the northeastern area, the common winds blow between northwest and northeast. Gales may be experienced for 10% of the time during the winter, dropping to 2% in July and August, sometimes arriving with little warning and rapidly building to gale force.

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