The dry season runs from May to October and is the best time to visit for most purposes. Days are sunny, roads are passable, wildlife concentrates around water, and the lake is calm and clear. July and August are the coolest months — pleasant in the highlands, though nights can be cold at altitude (bring a layer for Nyika or Mulanje). September and October heat up again, but remain dry.
May to August is the sweet spot: game viewing peaks as vegetation thins, the Shire River at Liwonde is at its most productive, and the plateau hikes are comfortable. This is also the busiest period for accommodation at popular spots like Cape Maclear and Liwonde, though Malawi never gets truly crowded by East African standards.
The rainy season runs from November to April, with the heaviest rains in December, January, and February. Flooding is common, rural roads become impassable in places, and malaria risk is higher. Wildlife disperses widely in the parks and game viewing suffers. That said, the landscape is vivid green, bird life peaks with the arrival of migrants from the north, and prices and crowds both drop. If birding is your focus, the rainy season has its rewards.
October is a shoulder month with some advantages: game viewing is still excellent, the heat is building but manageable, and the Mulanje area is dry before the early-season rains hit the highlands. Orchids bloom on Nyika Plateau in October and November.
Lake Malawi can be swum year-round, though the lake is roughest from June to August when the mwera wind picks up, particularly in the south. Visibility for snorkelling and diving is best from August to November.