<P> The Sahel climate or tropical dry climate, is the predominant climate type in the northern part of Nigeria . Annual rainfall totals are lower compared to the southern and central part of Nigeria . The rainy season in the northern part of Nigeria last for only three to four months (June--September). The rest of the year is hot and dry with temperatures climbing as high as 40 ° C (104.0 ° F). </P> <P> Alpine climate or highland climate or mountain climate are found on highlands regions in Nigeria . Highlands with the alpine climate in Nigeria, are well over 1,520 metres (4,987 ft) above sea level . Due to their location in the tropics, this elevation is high enough to reach the temperate climate line in the tropics thereby giving the highlands, mountains and the plateau regions standing above this height, a cool mountain climate . </P> <P> Nigeria, like the rest of West Africa and other tropical lands, has only two seasons . These are the dry season and the rainy season . The dry season is accompanied by a dust laden airmass from the Sahara Desert, locally known as Harmattan, or by its main name, The Tropical Continental (CT) airmass, while the rainy season is heavily influenced by an airmass originating from the south atlantic ocean, locally known as the south west wind, or by its main name, The Tropical Maritime (MT) airmass . These two major wind systems in Nigeria are known as the trade winds . </P> <P> The tropical maritime airmass (MT) is responsible for Nigeria's rainy season . This wind (the tropical maritime airmass) invades the country from February in the southern part of Nigeria while it takes longer for the wind to fully cover the whole of the country, reaching the northern part of Nigeria in June . Its invasion is as a result of the northward retreat, of the tropical continental airmass (CT) known as the harmattan . The northward retreat of the tropical continental airmass (CT), is caused by the sun's northward shift from the tropic of capricorn in the southern hemisphere to the tropic of cancer in the northern hemisphere . This shift begins from February and ends in June, when the sun is fully overhead, at the tropic of cancer in the northern hemisphere . </P>

When does the southwest wind blow in nigeria