Timor-Leste has two seasons: a dry season from roughly May to November, and a wet season from December to April. The coast is hot year-round; the highlands are considerably cooler.
Dry season (May–November) is the best time to visit. Roads are passable, mountain trails are accessible, and days are clear. July and August are peak months — still manageable by Southeast Asian standards. This is also prime time for coffee tourism: the harvest runs May to September, and you can visit plantations and watch processing in action.
October to December is whale watching season. Timor-Leste lies on migration routes for sperm whales and blue whales, and sightings are common from the Dili waterfront or by boat. It is one of the better places in the region for this.
Wet season (December–April) brings daily downpours, flash floods, and serious road problems in the interior. Many mountain roads become impassable. On the coast, the sea stays warm and diving remains good — visibility can actually be better after rain clears the air. Dengue mosquitoes peak during the wet season; take precautions.
Diving and snorkelling are possible year-round but visibility is generally best in the dry season. Water temperature sits around 27–29°C throughout the year.
If you're coming specifically for Mount Ramelau, go between June and September when the trail is dry and the pre-dawn views are sharp.