The Harmattan is a dry easterly or northeasterly. Crossing the Sahara, it picks up sand and dust as it rages out over the West African coast. The fine dust carried by the Harmattan can travel hundreds of kilometres over the sea, interfere with the machinery of aircraft and coat the decks of ships.
This wind is strongest between November and March. In summer the cooler southwest winds of the monsoon can push beneath it and raise it aloft, causing tornadoes over western Africa.