Dhaka is defined by a tropical monsoon climate, a dynamic system characterized by wide swings in humidity and rainfall. The year is traditionally divided into three primary seasons: the cool, dry winter; the scorching pre-monsoon spring; and the heavy, humid monsoon summer.
Seasonal Climate Dynamics
The Cool Dry Season (November – February)
This is the most stable and pleasant time in the capital. The air is remarkably dry, and skies remain clear for weeks.
- Morning Mist: In December and January, early morning fog is common, occasionally thick enough to disrupt river transport and flights.
- Evening Chill: While daytime highs hover around 25°C (77°F), the lack of humidity causes temperatures to drop quickly after sunset, often reaching 12°C to 15°C (54°F–59°F).
- Recent Trends: Historically mild, recent years have seen more frequent "cold waves" where northerly winds bring temperatures down toward 8°C (46°F), which feels much colder due to the lack of insulation in local architecture.
The Pre-Monsoon Heat (March – May)
As spring arrives, the climate shifts into a period of "relentless sun." April and May are typically the hottest months of the year.
- The Heat Index: Temperatures frequently exceed 36°C (97°F), but the rising humidity makes the "feels like" temperature climb into the mid-40s.
- Kalbaishakhi (Nor'westers): Late afternoons often bring sudden, violent thunderstorms known locally as Kalbaishakhi. These localized storms bring intense rain, lightning, and dust, providing brief relief from the oppressive heat before the humidity returns.
The Monsoon Season (June – Early October)
Nearly 80% of Dhaka’s 1,850mm of annual rainfall occurs during this window. The southwest monsoon brings a consistent, thick cloud cover that lowers peak temperatures slightly but keeps the humidity at near-saturation levels (80%–90%).
- Rain Patterns: It is rarely a constant drizzle; it is more often characterized by intense, multi-hour downpours followed by humid lulls.
- The Urban Sensation: The weather feels "heavy" and oppressive. Even when rain isn't falling, the moisture in the air prevents sweat from evaporating, making any physical activity feel strenuous.
The Urban Microclimate
Dhaka experiences a profound Urban Heat Island (UHI) effect. Because of its extreme population density and lack of green space, the central urban core can be up to 10°C (18°F) hotter than the surrounding rural countryside. Areas with corrugated iron roofing, such as informal settlements, trap heat intensely, leading to a microclimate where the night never truly cools down.
Historical Context and Local Adaptation
Dhaka sits on the lower reaches of the Ganges Delta, making it historically prone to flooding. In response, locals have traditionally adapted through architecture and lifestyle:
- Daily Rhythms: During the hot months, the city is most active in the early morning and late evening to avoid the midday sun.
- Architecture: Older buildings often feature high ceilings and thick walls to naturally regulate heat, though modern high-rises now rely heavily on air conditioning, which ironically exacerbates the outdoor heat island effect.
- Monsoon Preparedness: Residents are accustomed to "waterlogging," where streets temporarily flood during heavy rains. Life continues with remarkable resilience, using rickshaws and specialized footgear to navigate the flooded lanes.
Unique Weather Phenomena
- Tropical Cyclones: While Dhaka is inland, it is in the path of cyclones originating in the Bay of Bengal. These mostly affect the city in two windows: April–May and October–December, bringing sustained heavy winds and prolonged rainfall.
- Atmospheric Pressure: In the monsoon, the station pressure drops significantly as moisture-bearing winds rush in from the Indian Ocean, a shift that locals often "feel" in the joints or through a general sense of lethargy before a storm breaks.