Yearly rainfall varies between 2300 and 4000mm (90-160in), most of the rain falls between December and March (Overdorff, 1993). Average annual temperature is 21°C (70°F), with anual lows occurring between June and September and reaching 4°C (40°F).
Ranomafana National Park is a cloud forest. Curiously enough the "dry" season (June through September, austral winter) actually seems wetter than the "wet" season (December through March)-- in July there is a continual cold, grey drizzle, while January gets late-afternoon /evening cloud bursts. Those cloud bursts can dump 50mm of rain in a night.
Sometimes the wet season brings a cyclone, which in the past has washed the bridge to the park away. These cyclones can have a tremendously destuctive impact on the trees of the forest.
The most pleasant months (those with the least chance of rain and a pleasant temperature) are probably October and November.
Killing frosts happen some winters and destructive hailstorms are common. (Wright, 1999)
Overdorff, D. J., 1993, "Similarities, differences, and seasonal pattern in the diets of Eulemur rubriventer and Eulemur fulvus rufus in Ranomafana National Park, Madagascar", International Journal of Primatology, 14: 721-753
Wright, P., 1999, "Lemur Traits and Madagascar Ecology: Coping with an Island Environment", Yearbook of Physical Anthropology, 42: 1-42