The harmattan is a northeast or easterly wind blowing from the Sahara toward the Gulf of Guinea during the boreal winter (November–March). It carries enormous quantities of mineral dust that can reduce visibility below 1 km and cross the Atlantic as far as the Caribbean.
Effects on West Africa
Although dry and dusty, the harmattan provides relief from humid tropical heat by lowering night-time temperatures. However, it causes respiratory problems, damages crops, and hinders aviation. The harmattan's "dry haze" differs from Mediterranean calima by its higher dust concentration and lower moisture content.