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Harmattan

Harmattan, hot, dry wind that blows from the northeast or east in the western Sahara and is strongest in late falland winter (late November to mid-March). It usually carries large amounts of dust, which it transports hundreds ofkilometres out over the Atlantic Ocean; the dust often interferes with aircraft operations and settles on the decksof ships.

The harmattan is a trade wind strengthened by a low-pressure centre over the north coast of the Gulf of Guineaand a high-pressure centre located over northwestern Africa in winter and over the adjacent Atlantic Oceanduring other seasons. In the summer it is undercut by the cooler winds of the southwest monsoon, blowing infrom the ocean; this forces the harmattan to rise to an altitude of about 900 to 1,800 metres (about 3,000 to 6,000feet). The interaction between the harmattan and the monsoon sometimes produces West African tornadoes.