Bangladesh experiences a tropical monsoon climate, characterized by significant seasonal variations in rainfall, high temperatures, and high humidity. The climate is relatively consistent across the country, with only minor regional differences. The year is typically divided into three seasons: a hot and humid summer from March to June, a rainy and humid monsoon season from June to November, and a warm-to-hot, dry winter from December to February. During summer, maximum temperatures generally range from 38°C to 41°C (100.4°F to 105.8°F), with April being the hottest month. January, the coolest month, sees average temperatures between 16°C and 20°C (61°F to 68°F) during the day, with nighttime temperatures around 10°C (50°F).

In winter, winds generally blow from the north and northwest, moving at a speed of 1 to 3 kilometers per hour (0.6 to 1.9 mph) in northern and central areas, and 3 to 6 kilometers per hour (1.9 to 3.7 mph) near the coast. From March to May, violent thunderstorms, called “northwesters,” bring winds of up to 60 kilometers per hour (37.3 mph). Intense storms in early summer and late monsoon season can produce southerly winds of over 160 kilometers per hour (99.4 mph), resulting in waves up to 6 meters (19.7 feet) high in the Bay of Bengal, often leading to disastrous flooding in coastal areas.

Rainfall is a dominant feature of Bangladesh’s climate, causing annual flooding. Except for the relatively dry Rajshahi region, where annual rainfall is about 1,600 mm (63 inches), most parts of the country receive at least 2,300 mm (90.6 inches) of rainfall annually. The Sylhet region, located in northeastern Bangladesh, receives the highest rainfall due to its proximity to the foothills of the Himalayas. From 1977 to 1986, annual rainfall in Sylhet ranged from 3,280 mm to 4,780 mm (129.1 inches to 188.2 inches). Humidity in Bangladesh varies seasonally, with average daily humidity levels ranging from 55% to 81% in March to 94% to 100% in July.

Approximately 80% of Bangladesh’s rainfall occurs during the monsoon season, which is driven by the contrasts in air pressure caused by the differential heating of land and water. In the hot months of April and May, hot air rises over the Indian subcontinent, creating low-pressure areas into which cooler, moisture-laden winds from the Indian Ocean rush. This marks the beginning of the southwest monsoon, which starts in June and lasts until September. The monsoon divides into two branches: one that strikes western India and another that moves up the Bay of Bengal, affecting Bangladesh and northeastern India before being turned westward by the foothills of the Himalayas.

Bangladesh is prone to various natural disasters, including floods, tropical cyclones, tornadoes, and tidal bores, especially in the coastal belt. These calamities strike almost every year, causing significant loss of life and property. Between 1947 and 1988, 13 severe cyclones hit the country. In May 1985, a cyclonic storm with winds reaching 154 km/h (95.7 mph) and waves as high as 4 meters (13.1 feet) killed over 11,000 people, destroyed 94,000 houses, and damaged nearly 400 kilometers (248.5 miles) of embankments.

Flooding, which occurs annually due to the monsoons, leads to loss of life, damage to infrastructure, and a shortage of drinking water, contributing to the spread of diseases. In 1988, two-thirds of Bangladesh’s 64 districts were affected by floods caused by heavy rains. The flooding left millions homeless and without clean water, and disrupted essential services like transportation and relief efforts. For example, half of Dhaka, including the runway at Shahjalal International Airport, was inundated. The 1989 tornado, which killed over 600 people, further exacerbated the country’s vulnerability to natural disasters.

Efforts to combat cyclones and tidal bores include early warnings and providing safe public buildings for shelter, but infrastructure to adequately address these challenges was still underdeveloped by the late 1980s. The Third Five-Year Plan (1985-1990) focused on improving meteorological forecasting capabilities, particularly through agrometeorology, marine meteorology, oceanography, and hydrometeorology, with support from the United Nations Development Programme.

Cold weather is rare in Bangladesh, but when temperatures drop below 8°C (46°F), those living in inadequate housing or without warm clothing are at risk of hypothermia or death.