The Inter-Tropical Convergence Zone

The greatest amount of rain falls across the coast of West Africa. Here rainfall can exceed 2000mm per year. The further north you go, the less rain, so in the Sahara desert there is less than 250mm per year.

Along the coast, rain falls in every month, because it has an equatorial climate. But just north of the coast there is one month dry season. The dry season becomes longer the further north you go. So in Nigeria, it is 9 months and in the Sahara it is 12 months Nigeria

West Africa there are 2 main wind directions – SW and NE Rainfall is determined by wind direction South Westerly Winds These are brought by Tropical Maritime (mT) air streams They are trade winds The are onshore winds The blow from the Atlantic Ocean These bring rainy, thundery weather North-Easterly Winds Brought by Tropical Continental (cT) air streams They are trade winds The are offshore winds They blow from the Sahara Desert They bring very warm, dry, dusty weather

The SW and NE trade winds blow towards the Equatorial Low Pressure, this is the ITCZ The ITCZ moves with the overhead sun, because where the sun is overhead should be the hottest area. The ITCZ is over the Tropic of Capricorn in Africa on December 21 Land, heats up a lot quicker than oceans so the ITCZ follows the coast of Africa instead of going into the Atlantic Ocean On June 21 the ITCZ is over the Tropic of Cancer N – Tropic of Cancer 23.5 S – Tropic of Capricorn January

23.5 N – Tropic of Cancer 23.5 S – Tropic of Capricorn 0 January

23.5 N – Tropic of Cancer S – Tropic of Capricorn June

Remember! When the ITCZ is north of countries in Africa, they will be receiving the rain brought by the Tropcial Maritime air stream, so countries on the West Coast of Africa will always have wet weather because the ITCZ is always north of it! These countires will have 12 months wet season. Countries just north of the coast will have 11 months wet season because the ITCZ is only north of these countries for 11 monhts of the year. The Sahara desert will have 0 months wet season because the ITCZ is never north of it!

12 months wet season 11 months wet season 0 months wet season