Loango is humid year-round, but the drier months from roughly June to September are generally easier for travel and wildlife outings. Humpback whales pass offshore in season, while the wetter months can make the forest lush and atmospheric but also complicate tracks and transfers.
If you are coming for a specific experience such as gorilla tracking, turtle nesting, or whale watching, plan the trip around that season rather than assuming all wildlife is equally visible at any time.