There are only two seasons in Madagascar : Dry season and wet season. Wet season lasts in most areas 5 months ( from December to April). In eastern Madagascar, it rains quite often all year long whereas it rarely rains in western Madagascar.
On the central parts of Madagascar, winter nights are so cold that the temperature may go down to +5°C. It may even go down to around freezing point in Antsirabe. So please bring warm clothes if you travel to Madagascar from May till September. From November till March, it is hot in the coastal Areas of Madagascar. The temperature in the coastal regions is generally higher than that in Antananarivo.
Overall, Madagascar is best experienced between the cool months of April and December. These months are safe from cyclones and are cooler in temperature. July and August are considered as "peak seasons" because tourists start to flock at these months because of the holidays.