Madagascar is the fourth largest island in the world, separated from the African continent by the Mozambique Channel. It has several climatic zones depending on the altitude and location, but in general, the climate is subtropical, with a hot and rainy season between November and April (summer), and a cooler dry season from May to October (winter).
The period between May to October (winter in the Southern Hemisphere) is the best time to travel to Madagascar, with cooler temperatures and little rain. The months of July and August are peak high season, also the coolest months of the year, although during this time many reptiles and small mammals are hibernating. If reptile sighting is what you seek, warmer months of September and October may be better for you.
The only time you should avoid is January to March, when heavy rain can make many roads muddy and impassable. Keep in mind that temperatures are much cooler in the highlands and if you are travelling to the Eastern region, do not forget your rain gear: rainfalls are expected all year long.