Madagascar experiences most rainfall between December and March.
The country is also affected by the cyclone season in the Indian Ocean during this period, which naturally makes late April through to early November as the better season to visit Madagascar.
However, being such a big island does mean that there are geographical climate differences and the best time to travel may depend on your particular areas of interest.
October and November is a particularly excellent time for seeing baby lemurs, whale watching is at its peak from July through to October and whale sharks can be seen from October through to the end of November.
April is viewed as low season but you will enjoy quiet parks and a green landscape, though we have found in the past that certain areas can be closed in the early part of the season if extensive cyclone damage is caused during the rainy season.
Overall therefore one can consider travel anytime from April through to November with optimum conditions being from September onward. Whenever you choose to travel however you should pack for all weather conditions.