Then, there is a very hot period from March to May, before the monsoon, when the temperature can reach or exceed 40 °C (104 °F) in the worst moments, and a rainy season from June to mid-October, characterized by stifling weather, widespread cloudiness and frequent rains. From mid-October to mid-November, before the winter, there is a period lasting one month with good weather and high temperatures, around 30 °C (86 °F).
The monsoon season goes roughly from June 5 to October 15, but already in May (and more rarely in April), the first showers in the afternoon can occur. From mid-April to early December, Calcutta can be affected by cyclones, tropical storms coming from the Bay of Bengal, with a higher chance at the beginning and at the end of the period, namely from April to June and in October-November.
The Bengal region is particularly prone to flooding because of the conformation of the territory (we are in the area of the huge Ganges-Brahmaputra delta, and the river of the city, the Highly, is a branch of the Ganges). South of Calcutta, the sea is warm enough for swimming throughout the year, although it drops to 23/24 °C (73/75 °F) in January and February.
In November and in the first half of December, the rains have usually ceased, but now and then a cyclone can still affect the area.