The dry season from late November to early March is the most comfortable time and also the best for birdwatching, when the Siberian and Central Asian migrants arrive at the bird sanctuary. December and January are peak tourist months and the most expensive.
The pre-monsoon months of April and May are very hot and humid; the southwest monsoon proper runs June through August, with daily downpours but lower prices and lush green landscapes — some travellers consider it the best time to visit Kerala. The Onam festival and the snake boat races fall in August or September. Avoid late September and October if you can; the weather is unsettled and the water sometimes too high for safe boat travel.