Mediterranean Winds

Sirocco - Scirocco - Jugo Wind

From Treccani Enciclopedia Italiana:

Scirocco: Vento di Sud-Est. Tipico lo scirocco del Mediterraneo, che soffia dal Sahara come vento caldo e secco, ma giunge sulle coste italiane o francesi come vento caldo umido poiché, superando il mare, si è arricchito di  umidità.

È così detto anche il punto della rosa dei venti da cui soffia lo scirocco., il Sud-Est.

Technical description:

Sirocco (scirocco; jugo): This term is an all-inclusive name given to warm (or hot) southeast to southwest winds originating in the hot, dry air masses over Libya and Egypt, flowing northward into the south-central Mediterranean basin.  

Siroccos occur as a result of surface and upper level depressions moving eastward across the southern Mediterranean Sea or north Africa. The air flows northward from the Sahara desert, south of Tunisia, as well as from Libya and Egypt, producing hot, dry and dusty conditions over the northern African coast, resulting in poor visibility and damage to instruments and equipment. As it travels northward, the Sirocco builds moisture and clouds, causing fog and rain within the northern Mediterranean regions such as Italy and Greece. The onset of a gale-force Sirocco often occurs as a surface low moves into the Gulf of Gabes from Tunisia, combined with the passage of a deep 500 mb trough extending well into north Africa and positioned west of the Gulf of Gabes. The gale-force Sirocco is most common during the spring.

The Kvarner

The Scirocco sometimes affects the Adriatic Sea area but more frequently in the southerm part and appearing as a local wind. It normally occurs within the warm sector of a cyclone passing either north or west of the region. These cyclones originate either over North Africa or south of the Alps, primarily in the Gulf of Genoa in the latter case.

The Scirocco tends to occur year-round without a favored month or season. Between March and June it blows in the north as well. Differing from the bora, the scirocco its not sudden and tempestuous. The winds and seas during a scirocco build gradually over a 36-38 hour period in a predictable fashion, and there is usually adequate time for sailors to take defensive measures. However, winds can reach gale force (greater than or equal to 34 kt), especially in winter and spring. It wavers for days without haste, and even if in most cases it carries rain, the intensity is weak and duration only a few hours so that it poses little problem for boating. It  has unchanging direction and even force and thus, like the maestral, it is favourable for sailing. 

It enters the Kvarner with high waves that in extreme cases come all the way from the Strait of Otranto. It is most dangerous in the area of Kvarneric/Quarnerolo, where the nautical tourists in their attempts to flee from the open sea, hope to find calmer waters. But here the scirocco gets into a rage, feeling perhaps it would lose its strength soon after Plavnik.

The average duration of continuous gale force winds during a Scirocco is 10 to 12 hours and occasionally as long as 36 hours. The maximum wind speed likely during a Scirocco is about 55 kt. Local terrain features alter the effect of the Scirocco. Winds will parallel the coast in general. 

As a cold front approaches from a relatively flat, low surface, such as the ocean, toward an elevated land mass, super-gradient winds will occur due to the Venturi effect. These winds are restricted to a narrow band between the front and the landmass and do not normally sustain for long periods of time. Seas are usually not high with strong southeasterlies due to protection from the terrain, but sustained Scirocco winds can raise seas of 6.6 to 9.8 ft (2 to 3 m) in the open water west of Koper. Waves in the harbor are fetch limited. 

The jugo or scirocco and lebic also have a high frequency during the winter season, and these do raise high seas at anchorage locations in Zadarski Kanal. The winds of a "severe" jugo having speeds of greater than 34 kt (17.5 ms-¹) last only about 5 hours, but on exception, can extend to 25 hours. Strong jugos with winds from 21 -34 kt (10.8 - 17.5 ms-¹) have an average duration of 19 hours, and with exception to 36 hours. The highest mean hourly wind speed for a jugo in the Adriatic, based on data from 1958-1987, was 53 kt (27.3 ms-¹). This occurred on 21 March 1971.






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Created: Thursday, June 20, 2002; Last updated: Tuesday, October 16, 2012
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