The climate of Guinea is tropical with two alternating seasons—a...

The climate of Guinea is tropical with two alternating seasons—a dry season (November through March) and a wet season (April through October). The arrival of the migratory intertropical convergence zone (ITCZ) in June brings the heaviest rainfall of the wet season. As the ITCZ shifts southward in November, the hot, dry wind known as the harmattan blows from the northeast off the Sahara.

On the coast a period of six months of dry weather is followed by six months of rain. The average rainfall at Conakry is 170 inches (4,300 mm) a year, and the average annual temperature is about 81 °F (27 °C). In the Fouta Djallon, January afternoon temperatures range between 86 and 95 °F (30 and 35 °C), while evening temperatures dip to 50 °F (10 °C). Rainfall varies between 63 and 91 inches (1,600 and 2,300 mm) annually, and the average annual temperature is about 77 °F (25 °C).

In Upper Guinea rainfall drops to about 59 inches (1,500 mm) a year. During the dry season temperatures of more than 104 °F (40 °C) are common in the northeast. In the Forest Region at Macenta, there may be 106 inches (2,700 mm) of rain annually. Only the months of December, January, and February are relatively dry, each having less than one inch of precipitation. At low altitudes, temperatures resemble those of the coastal areas.

http://www.britannica.com/eb/article-55205/Guinea