The Republic of the Congo straddles the equator, with the north running into the great central African rainforest and the south opening onto savanna. The country has two wet and two dry seasons; the timing flips as you cross the equator.
Long dry season in the south (May–September) is the best window for visits to Brazzaville and the southern parks. Days are warm but not punishing, and the roads are usable. This is also when gorilla tracking in Odzala-Kokoua National Park, in the north, is at its best — the bais and saline clearings draw animals in.
Short dry spell (December–January) gives another good window of weather across most of the country, useful for shorter trips.
Wet seasons (October–November and February–April) bring heavy daily storms. The forest is at its most alive, but roads outside Brazzaville become impassable and small-plane access to the parks is unreliable.
Odzala visits are typically multi-day operations booked through a single concession-holder; arrange well in advance. Yellow fever vaccination is required. Bring strong insect repellent — malaria is widespread.