The best time to visit Conakry is the dry season, from November to May. December and January are the coolest months, with daytime temperatures around 30°C and lower humidity, and the harmattan winds from the Sahara push a dry haze over the coast. February through April warms steadily into the high 30s.
Avoid June through October if you can — these are the rainy season months, when monsoon storms can drop hundreds of millimetres in a single day. Conakry has poor drainage, the roads flood routinely, and the chaos of getting around becomes much worse. August is the rainiest month of all, with rain on most days.
Independence Day (2 October) and the Tabaski celebrations (varying date in the Muslim calendar) are good times to be in the city for atmosphere, though many businesses close.