Temperatures vary little in Malaysia, hovering constantly at or just above 30°C by day, while humidity is high year-round. Showers occur year-round too, often in the mid-afternoon, though these short, sheeting downpours clear up as quickly as they arrive. The major distinction in the seasons, and worth bearing in mind when considering the best time to visit, is the arrival of the northeast monsoon (ushering in what is locally called the rainy season). This particularly affects the east coast of Peninsular Malaysia and the western end of Sarawak, with late November to mid-February seeing the heaviest rainfall.
On the Peninsula’s west coast and in Sabah, September and October are the wettest months. Monsoonal downpours can be heavy and prolonged, sometimes lasting two or three hours and prohibiting more or less all activity for the duration; boats to most islands in affected areas won’t attempt the sea swell at the height of the rainy season. In mountainous areas like the Cameron Highlands, the Kelabit Highlands and in the hill stations and upland national parks, you may experience more frequent rain as the high peaks gather clouds more or less permanently.
The best time to visit most of the region is generally between March and early October, when you will avoid the worst of the rains and there’s less humidity, though air pollution, usually caused by forest fires in Indonesia, can cause hazy conditions and even cancel flights. Despite the rains, the months of January and February are rewarding, and see a number of significant festivals, notably Chinese New Year and the Hindu celebration of Thaipusam. Visiting just after the rainy season can afford the best of all worlds, with verdant countryside and bountiful waterfalls, though there’s still a clammy quality to the air. Arrive in Sabah a little later, in May, and you’ll be able to take in the Sabah Fest, a week-long celebration of Sabahan culture, while in Sarawak, June’s Gawai Festival is well worth attending, when longhouse doors are flung open for several days of rice-harvest merry-making, with dancing, eating, drinking and music.