<P> This climate, the tropical savanna climate exhibits a well marked rainy season and a dry season with a single peak known as the summer maximum due to its distance from the equator . Temperatures are above 18 ° C (64 ° F) throughout the year . Abuja, Nigeria's capital city found in central Nigeria, has a temperature range of 18.45 ° C (65.21 ° F) to 36.9 ° C (98.4 ° F), and an annual rainfall of about 1,500 mm (59.1 in) with a single rainfall maxima in September . </P> <P> The single Dry season experienced in this climate, the tropical savanna climate in central Nigeria beginning from December to march, is hot and dry with the Harmattan wind, a continental tropical (CT) airmass laden with dust from the Sahara Desert prevailing throughout this period . </P> <P> With the Intertropical Convergence Zone (ITCZ) swinging northward over West Africa from the Southern Hemisphere in April, heavy showers coming from pre-monsoonal convective clouds mainly in the form of squall lines also known as the north easterlies formed mainly as a result of the interactions of the two dominant airmasses in Nigeria known as the Maritime tropical (south westerlies) and the Continental tropical (north easterlies), begins in central Nigeria while the Monsoons from the south atlantic ocean arrives in central Nigeria in July bringing with it high humidity, heavy cloud cover and heavy rainfall which can be daily occurrence lasting till September when the monsoons gradually begin retreating southward to the southern part of Nigeria. Rainfall totals in central Nigeria varies from 1,100 mm (43.3 in) in the lowlands of the river Niger Benue trough to over 2,000 mm (78.7 in) along the south western escarpment of the Jos Plateau . </P> <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>

When does the south west wind blow in nigeria