Including a description of the climate and weather of Gambia and Guinea-Bissau.
Senegal is on the west coast of Africa between 12° and 16°N. Its northern border with Mauritania is along the Senegal River. It has an eastern border with Mali and a southern border with Guinea and Guinea-Bissau. It encloses the Gambia on three sides.
Senegal has a tropical climate with a single short rainy season between June and September at the time of high sun. Temperatures are high throughout the year but there is a relatively cooler period from December to April during which rain is very rare.
The following description of the climate and weather of Senegal is also applicable to Gambia and Guinea-Bissau. All three countries are low-lying with very little land higher than 200 m/650 ft above sea level.
The chief factors controlling the climate of these countries are latitude and distance from the sea. Rainfall increases from north to south in Senegal. The north of the country is affected by the intertropical belt of cloud and rain between June and September; during these months rain only falls on twenty to thirty days and the average annual rainfall is about 300-350 mm/12-14 in.
In the south annual rainfall increases to between 1,000-1,500 mm/40-60 in and falls on between sixty and ninety days. Here the rainy season extends into October. The table for Dakar shows that, in the centre of the country, rainfall amounts are between these two extremes. Northern Senegal, on the edge of the Sahara, experiences conditions similar to the Saharan districts of Mali and Mauritania.
There is a marked seasonal contrast between the wet season, when winds are from the southwest and west, blowing from the South Atlantic, and the dry season, when they blow from the northeast out of the Sahara. The southwesterlies are warm and humid while the northeasterly harmattan wind is hot and dry and frequently dust-laden.
This contrast can be seen in the values for the relative humidity at Dakar and also those for Banjul in Gambia; both these stations are on the coast and the humidity is increased by the frequent sea breezes. Inland the humidity is much lower during the time of the harmattan. Temperatures are also considerably higher inland than on the coast during the dry season, but they fall lower at night.
The climate of Senegal is most oppressive during the wet season, particularly on the coast, where there is a combination of high humidity and high night-time temperatures. Hours of sunshine average nine to ten a day throughout the year; sunshine hours are lower on the coast, where there is more cloud than in the higher parts during the dry season.
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