November to February is the best time to visit. The monsoon has ended, temperatures are comfortable (20–27°C), the air is relatively clear, and the city functions at something approaching its best. Winter mornings in Dhaka have a pleasantly mild quality — cool enough for tea on a rooftop, warm enough to need no coat. This is also when cultural events and festivals concentrate.
March to May is increasingly hot — temperatures reach 35–40°C by April and May, and the pre-monsoon humidity makes it physically challenging to be outside during midday. The city can feel oppressive in this season.
June to September is monsoon season. Dhaka receives 2,000mm of rain annually, much of it in these four months. Flooding is regular and sometimes severe — streets become rivers, traffic halts, and low-lying areas in the old city go underwater. It is not the best time to visit for comfort or practicality, though the rain does reduce the dust and air pollution that characterises the dry months.
October is the transitional month — the monsoon ending, temperatures dropping, Eid celebrations sometimes falling in this period depending on the Islamic calendar. Eid ul-Adha and Eid ul-Fitr bring the city to a halt as millions return to their home districts: interesting to observe, but public transport and accommodation are strained.