Equatorial Guinea sits on and just below the equator, so there's no real cold season — only a perpetual contest between rain and heat. The mainland (Río Muni) and the islands (Bioko, Annobón) have different patterns.
Bioko Island dry season (November–March) is the practical window for visits to Malabo, the Pico Basile volcano, and the southern beaches where sea turtles nest. Days are warm (28–30°C) and humid, but rain is intermittent rather than constant. Turtle nesting on Ureca beach runs roughly October–February.
Mainland short dry seasons (December–February and June–August) are the better times for the Río Muni interior. Bata is hot and humid year-round, but roads are passable and the equatorial forest around Monte Alén National Park is accessible.
Wet seasons (April–May and September–November on Bioko, March–May and September–November on the mainland) bring intense daily rain. Roads turn to red mud, internal flights are unreliable, and the climate is genuinely oppressive.
Visas are bureaucratically tough — confirm requirements and have your hotel send a formal invitation before applying. Photography is sensitive throughout the country.