As discussed in an earlier article, some local weather phenomena have gained such a reputation over the years, either by its specific characteristics or by its intensity, that they have proven themselves to be worthy of their own name. After having dived into Mistral winds previously, today it is time to take a closer look at another famous wind in the Mediterranean, blowing from Northern Africa over the Mediterranean Sea: the Sirocco.
Introduction
The Sirocco, probably first mentioned by the Roman poet Horace, is a strong, dry, warm and dusty wind that blows from Northern Africa to the Mediterranean. The name Sirocco is derived from the Arabic word for ‘east’ and relates to the synoptic situation that is typical for the effect: a low pressure area usually tracks NE over the Mediterranean to provide Sirocco conditions. The Sirocco can be experienced throughout the entire year, but the highest likelihood and intensity usually take place during the spring. Italy and the Adriatic Sea are most regularly affected. Unlike many other specific wind phenomena, the name of the Sirocco depends locally, and is also known under some other names, describing the same phenomenon. An overview is found in Figure 1.
Figure 1: Map of the Mediterranean area displaying a selection of local names for the Sirocco. Figure generated with the help of ChatGPT, OpenAI.
Synopsis
Sirocco winds develop under low pressure conditions over the Mediterranean Sea. When the low tracks eastward over the Mediterranean, warm and dry air is blown from Northern Africa, specifically the Sahara, over the Mediterranean to Southern Europe (Figure 2). The original dry and warm air becomes increasingly moist when travelling over the Mediterranean and is therefore often experienced as warm and steamy at the European side of the Mediterranean Sea, instead of hot and dry.
Figure 2: Animation of the synoptic setting required for the development of Sirocco winds. Figure made by Weerplaza, one of Infoplaza’s brands.
Associated weather and effects
As the humidity levels of the originally dry air keep increasing over the Mediterranean Sea, saturation levels are often reached at the northern side of the Mediterranean. Consequently, Sirocco winds are typically associated with rain and cloudy weather at the Northern Mediterranean, with fog or mist events often taking place nearshore. Temperatures may easily exceed 40oC, and drop only mildly during nighttime, leading to sleepless nights for the local population.
In case of severe events, the Sirocco can blow constantly at gale force for a period of 1 to 1.5 days, with a force of 5-8 Bft (up to 40 kts). Those conditions can be experienced in many South European and even Middle Eastern countries.
Depending on the synoptics over Northern Europe, its effects may also be felt in more northerly regions in Europe. In case of high pressure over Scandinavia and continuous southerly winds, the Sirocco may reach Northern Europe as well. In these areas, the Sirocco is not specifically associated with weather conditions but can be related mainly to the Sahara dust. The dust is brought along with the wind at high altitudes and is then transported down to surface levels with rain showers, covering the area under a small layer of dust.
Effects at sea
Although best known for its effects onshore, the Sirocco can also be experienced by sailors on the Mediterranean. The relatively high wind speeds will elevate the waves consequently, posing a threat to anyone offshore. In the Adriatic Sea for example, waves reaching up to 5m are not uncommon. Next to the effect on the sea state, other risks arise by means of the Sirocco as well: the high temperatures accompanied with the Sirocco could lead to dangerous situations for offshore workers. Finally, the dust or fog accompanied with Siroccos can reduce the visibility, affecting offshore work as well.
Conclusive remarks
The Sirocco is a warm and dry wind in the Mediterranean area, with increasing humidity levels towards Europe. An eastward moving low pressure area is required in the Mediterranean, allowing a northerly wind flow. When reaching Europe, the wind has become moist and can often be associated with fog or mist nearshore. With wind speed up to 40 kts and the heat associated with it, the wind is often experienced as unpleasant, and dangerous for sailors and offshore workers.
In a few weeks’ time, this series will be continued with another wind phenomenon, that is probably less-known by the large public and takes place at the Caspian Sea: the Bautino-effect. For more information, in-depth articles or updates related to this week's North Sea weather, please look at our website.
