This article is reproduced from Lonely Planet.
Year-round travel is possible. Rain falls fairly evenly throughout the year and the difference between the main October to April rainy season and the rest of the year is not that marked. The exception is the east coast of Peninsular Malaysia, which receives heavy rain from November to mid-February. During these months many east-coast resorts close and boat services dwindle or stop altogether. Travel along the west coast is not affected. The states of Sabah and Sarawak receive high rainfall throughout the year, but it is heaviest from October to March.
As always, visit www.audioguidemalaysia.com for the best and only audio guides to Malaysia.