June to September is the busiest wildlife season, when humpback whales gather off the Manabí coast and many Isla de la Plata trips combine birding, snorkelling, and whale watching. The sea can be choppier in the dry season, but the wildlife payoff is high.
December to April is warmer and sunnier on the coast, with better beach weather and a more relaxed pace outside Ecuadorian holiday periods. Bring sun protection in any season; the dry tropical forest around Machalilla gives less shade than the word "national park" might suggest.