The climate of Manas is moist tropical with an annual rainfall between 3000 mm to 4000 mm. The climate can be divided into four distinct seasons based on the variation in the rainfall, temperature and winds. These are as follows:-
- Winter (December – February): Characterized by cool weather and fog. The temperature remains 20°C + 5°C. January is the coldest month. Average total rainfall is 114 mm with relative humidity of 77% + 5.
- Pre-monsoon (March – May): It is a transitional period between relatively dry winter and hot summer and is characterized by a rapid rise in temperature. As the season advances, the amount and frequency of rainfall increases due to frequent thundershowers with hailstorms. Average total rainfall during the season is 518.70 mm. The season is marked progressively by a greater number of cloudy days. Average temperature and humidity in this season are 23°C + 5°C and 70% + 5 respectively.
- Monsoon (June-September): It is the characteristic major rainy season of the year. The average monthly rainfall is 2860 mm. The average temperature during this season is 27.17°C with an average diurnal range of over 6°C. The humidity increases to 82% + 5. August is the hottest month.
d) Retreating monsoon (October-November): Towards the end of September, the monsoon weaken with an abrupt retreat followed by fair weather. With the advancing of the season the temperature falls and moving mist and fog appears. The average temperature is 27°C + 2. The average monthly rainfall is 1400 mm and the rainy days become fewer. Relative humidity is 82% + 5.
Rainfall pattern and distribution:-
Heavy rainfall is confined in between the period from June to September of the year. The average rainfall during monsoon period is 4000 mm and the mean annual rainfall is 3000 mm. The period from December to February is relatively dry with rare showers of (rainfall 120 mm).
Temperature pattern and distribution:-
The temperature seldom touches mercury level 400C and below 60C in the area. The hottest months are June-July; the temperature ranging in between 31-380C and the coldest is January.
Humidity pattern and distribution:-
The dry spell prevails during the period from November to March with relative humidity around 65 %. During the period from April to October the relative humidity swings as high as 86 % with a maximum of 94 % at times.
Wind speed pattern and distribution:-
The area experiences strong to moderately strong wind in the months of February-April. In other months the wind velocity is low.
Drought and its periodicity:-
There is practically no record of drought in the Park. The rainfall is, however, rare in the months from later part of December to February. But water scarcity is not acute during dry spell, owing to the presence of number of available perennial water sources.