Madagascar has two seasons, a warm, wet season from November to April, and a cooler dry season between May and October. However, different parts of the country have very different weather.
The east coast is hotter and wetter, with up to 4000mm of rainfall per year. In the rainy season, there are strong winds, and these can cause a lot of damage. Avoid visiting eastern Madagascar between January and March because the weather can make road travel very difficult. The dry season is cooler and more pleasant.