The climate of Bangladesh ranges from subtropical to tropical. The humidity remains high all year and reaches between 90%-95% from June to September. Bangladesh has three main seasons. The mild (70s [°F]) or cold season, from mid-October to the end of February, is characterized by sunny skies, drier weather, and cool (high 50s [°F]) evenings. During the hot season, from March until the end of May, there is quite a change. The early part is pleasant (75°F), but as the monsoon approaches, hot (95°F) temperatures and high humidity make life difficult. The monsoon season lasts from June to October. At the beginning of the monsoon, the continuous rains cool the atmosphere. Temperatures are milder (85°F to 90°F), but the humidity can be oppressive.
Tropical cyclones emerge from the Bay of Bengal with high winds and tidal waves on the average of one major cyclone every 3 years. There are two cyclone seasons, one just before the monsoon (May to June) and one just after the monsoon (October to November). Damage generally is limited to the southern finger of the country (east of Chittagong and Cox's Bazaar).
During the monsoon season in a normal year, about 30% of the country is under water. Some years, however, floods cover 70% of the country. At some times during the year, up to 70% of the country is under water. Annual flooding is a way of life but often the flooding is not due to rainfall but caused by water coming from across the borders via the Ganges, Meghna, and the Brahmaputra Rivers.