When is the best time of year to visit Chitwan?

Chitwan National Park is open year round with most wildlife visible. However during the 
end of the dry season in October to December there is a greater chance of seeing tigers and other wildlife as they come out to the waterholes. Local guides also mention November and December as being good times though it's not that hot. From June - to September it is both Nepal Hot season and Monsoon season. It can get very hot and humid in Chitwan at this time of year making trekking uncomfortable for many.