The Meenachil River basin experiences a tropical monsoon climate (Köppen classification: Am). The region is heavily influenced by two monsoon seasons: the Southwest Monsoon (Edavappathy) from June to August, and the Northeast Monsoon (Thulavarsham) from October to November.
Average temperatures range from 23°C to 34°C (73°F to 93°F) year-round, accompanied by high humidity, typically between 70% and 90%. Annual rainfall in the basin is substantial, often exceeding 3,000 mm (118 inches). Due to the steep gradient in its upper reaches and heavy monsoon downpours, the river is prone to sudden flash floods, which frequently inundate the lower plains and towns like Pala and Kottayam. The best time to visit the river and its surrounding backwaters is during the drier, cooler months from December to March.