The harmattan winds blow across the Sahara to the Gulf of Guinea and the Cape Verde Islands. The winds are very dry and dusty. This dryness makes fires more likely in harmattan season and can aggravate health conditions.
When the West African trade wind passes over the Sahara, it picks up fine particles of dust. The fine particles are transported long distances and can be quite dense, sometimes blocking out the sun. Millions of flights are diverted every year due to harmattan winds. The harmattan season is from the end of November to the middle of March. The winds are sometimes called "Doctor" due to the relief they bring from oppressive heat.