Guinea has a tropical climate with two distinct seasons: dry and wet. The best time to visit is during the dry season from November to April, when roads are passable, the skies are clear, and hiking in the Fouta Djallon is at its best.
The rainy season runs from May to October, with the heaviest rains in July and August. Conakry is one of the wettest capitals in Africa, receiving over 4,000 mm of rain annually, most of it in these months. During the rains, unpaved roads turn to mud, rivers flood, and travel times can double or triple. Some routes in the interior become completely impassable. The Fouta Djallon waterfalls are most impressive during and just after the rains, but getting to them is the challenge.
Temperatures are hot year-round. Coastal areas like Conakry hover between 25-32°C with high humidity. The Fouta Djallon highlands are notably cooler, especially at night -- Dalaba and Labe can drop to 15°C, a welcome relief. The eastern savanna around Kankan is the hottest part of the country, regularly exceeding 35°C in March and April.
The harmattan wind blows dry, dusty air from the Sahara between December and February, reducing visibility and giving the sky a hazy quality. It is not unpleasant but does make photography difficult.
If you are planning to hike the Fouta Djallon, aim for November to January -- the rains have just ended, the waterfalls are flowing, the landscape is green, and the trails are drying out.