The Chitwan National Park has a tropical monsoon climate, with height humidity all through the year, and three main seasons.

1. Summer
March to early June are the traditional hot months, with temperatures rising progressively to a peak in May. During April, despite the heat of the day the nights can be quite cold. South-westerly winds prevail, and relative humidity is lowest in March.

2. The Monsoon
Towards the end of May the pre-monsoon storms set in. Dark clouds mass in the afternoons, with thunder and lightning and high winds. If rain falls, it comes in late afternoon showers lasting perhaps only fifteen to twenty minutes. As May changes into June the showers come with increasing frequency.
When the monsoon proper begins, around the middle of June, it is another story. From then until late September the moisture-laden south-easterly winds weeping up from the Bay of Bengal bring heavy rain, and of the annual total of some 80 inches, more than 80 per cent falls in these three months.
Precipitation is not normally continuous, and often, in any monsoon month, there are as many dry days as wet ones. During the monsoon humidity is extremely high.

3. Winter.
Winter lasts from October to the end of February. The northerly winds are cool, coming down from the mountains, and this is the best time of the year to see the Great Himalayan Range, the air being particularly clear in November.
January is the coldest month, with temperatures falling almost to freezing-point, especially when it rains. From late November the relative humidity touches 100 percent in the mornings, and so there is dewfall during December and January nights and sometimes when you hear the drips pouring off the trees in the morning, it is often mistaken for rain. After an especially cold morning it is hard to believe that the temperature will rise to 20-25 Celsius in the afternoon.