The Harmattan is a dry and dusty West African trade wind. It blows south from the Sahara into the Gulf of Guinea between the end of November and the middle of March (winter). The temperatures can be as low as 3 degrees Celsius. The name comes from or is related to an Akan cognate.
On its passage over the desert it picks up fine dust particles (between 0.5 and 10 micrometres).
In some countries in West Africa, the heavy amount of dust in the air can severely limit visibility and block the sun for several days, comparable to a heavy fog. The effect caused by the dust and sand stirred by these winds is known as the Harmattan haze, which costs airlines millions of dollars in cancelled and diverted flights each year, and risks public health by increasing meningitis cases. The interaction of the Harmattan with monsoon winds can cause tornadoes. Humidity drops to as low as 15 percent and can result in spontaneous nosebleeds for some. The wind can cause severe crop damage.