Bangladesh has a typical monsoon climate with the same threefold division of the year that occurs in India, but the cool season (November to February) is generally warmer than India. During the hot season there are rainstorms, some thundery, and during the main rainy season (June to September) the rain is frequent and heavy. Generally, annual average rainfall varies from 1500 to 2500 mm (60 - 100 "), but near the eastern border this rises to 3750 mm (150 "). Rainfall from September to November is less reliable, but is occasionally very heavy and is usually associated with violent tropical cyclones that develop over the Bay of Bengal. Storm waves and sea surges raise the water level along the coast and in the numerous branching water courses of the delta so that widespread flooding of the low-lying areas takes place adding to the devastation caused by the strong wind. Such storms have led to great loss of life and destruction of crops on several occasions.

Although temperatures during the hot season are rather lower than in some parts of India, the heat is made uncomfortable by the high humidity. This damp, muggy season continues throughout the main rainy season, but the heat is rarely dangerous. It is, however, very unpleasant for the unacclimatized visitor. There is no great difference in temperature conditions around the year from one region to another. During the hot season, temperatures are a little higher inland (Dacca - April - average maximum temperature 35 °C / 95 °F) than on the coast (Chittagong - April - average maximum temperature 32 °C / 89 °F). Owing to the greater cloudiness of the rainy season, average daily sunshine hours are least between June and September (about four hours per day), but six - eight hours per day for the rest of the year.