Under the Köppen climate classification, City of Thrissur features a tropical monsoon climate (Am). Summer lasts from March to May which is the hottest time of the year. Summer months are uncomfortable due to higher levels of heat and humidity. Daytime temperatures can rise up to 36 to 38 °C (96.8 to 100.4 °F) coupled with excessive humidity. Summer is followed by the South-west monsoon from June to September. October and November form the post monsoon or retreating monsoon season. Winter from December through February is cooler, and windy, due to winds from the Western Ghats. Winter months are generally dry and less humid compared to other months of the year. Morning temperatures are usually cool and daytime temperatures hover around 30 °C or 86 °F.
The city is drenched in the monsoonal season by heavy showers. The average annual rainfall is approximately 3,100 millimetres or 122 inches. The South-west monsoon generally sets in during the last week of May. After July the rainfall decreases. On an average, there are 124 rainy days in a year. The maximum average temperature of the city in the summer season is 36 °C or 96.8 °F while the minimum temperature recorded is 27 °C or 80.6 °F. The winter season records a maximum average of 31 °C or 87.8 °F and a minimum average of 20 °C or 68 °F.