The dry season runs from mid-December through April, when days are sunny, winds are light, and visibility underwater is at its clearest. This is the high season for beach visitors and weekenders from Panama City, and the island fills up on Saturday and Sunday. Arrive Friday if you want a quieter experience.
The rainy season (May–November) brings afternoon showers and greener vegetation, but the mornings are often clear and the island is noticeably quieter. The sea can be rougher. The trade-off is worth it if you are coming specifically for whale watching: humpback whales migrate through the Pearl Islands channel between July and October, and sightings are common from the island's rocky headlands and on boat tours.
Avoid major Panamanian public holidays if you are sensitive to crowds — the island is a favourite long-weekend escape for Panama City residents and flights book out fast.