Bangladesh may experience four to six mild to moderate cold waves between November and January, with two to three of them potentially intensifying into severe cold waves, according to the Bangladesh Meteorological Department (BMD).
In its latest three-month long-range forecast, the BMD also predicted that two to four low-pressure systems may form over the Bay of Bengal, with one or two potentially developing into cyclones.
According to the forecast, cooler nights and early mornings are already signalling the arrival of winter, particularly in northern villages, where chilly winds and morning mist have become noticeable.
The forecast, signed by Md Mominul Islam, director (Current Charge) of the BMD and Chairman of its Special Committee on Long-Range Forecasting, said one or two mild cold waves may occur in December.
BMD Meteorologist Dr Muhammad Abul Kalam Mallik told BSS that cold waves would be more pronounced in the northern and western parts of the country, including areas of Rajshahi, Rangpur and Khulna divisions, where temperatures may fall to 8–10°C.
Moderate cold waves are likely in January, when one or two severe cold waves may also occur, with temperatures dropping to 4–6°C.
The BMD classifies temperatures of 8–10°C as a mild cold wave, 6–8°C as moderate, and 4–6°C as severe. Temperatures below 4°C are classified as extremely severe cold waves.
Moderate to dense fog may occur in river basins from late night until morning during the three-month period, while other areas may experience light to moderate fog. Dense fog could reduce the difference between daytime and nighttime temperatures, making the weather feel colder.
However, Dr Mallik attributed the possibility of a relatively warmer winter to the prevailing El Niño conditions and rising global temperatures, whose effects are also being felt across South Asia.
He said cold waves would occur, but their timing, frequency and duration, particularly those of extremely severe cold waves, would likely remain limited.
"Overall, we expect a somewhat warmer winter this year," he said, cautioning that uncertainty remains over the frequency and duration of cold spells.
Regarding cyclones, Dr Mallik said October and November are generally cyclone-prone months in Bangladesh. Low-pressure systems frequently develop over the Bay of Bengal during this period, sometimes intensifying into cyclones.
He explained that the southward movement of the Sun shortens daytime hours and lengthens nights, while increased solar radiation raises sea surface temperatures in the Bay of Bengal, creating favourable conditions for such systems.
The BMD forecast also predicted normal rainfall across the country during the November-January period.
In November, Chittagong may receive the highest rainfall, at 35–40mm, followed by Barishal with 30–40mm. Dhaka, Sylhet and Khulna may receive 15–25mm, Mymensingh and Rajshahi 10–15mm, and Rangpur 4–8mm.
Rainfall is expected to decline in December and January. Dhaka may receive 8–10mm in December, while Sylhet may get 10–15mm. In January, Khulna may receive 10–14mm, while Dhaka and other divisions are likely to receive 6–10mm.
The BMD said the long-range forecast was prepared using meteorological data, upper-air weather patterns, climate models and forecasts from international centres approved by the World Meteorological Organization. El Niño and La Niña conditions were also taken into consideration.
Dr Mallik said historical data from 1948 to 2025 showed that an average of one to three low-pressure systems form over the Bay of Bengal during October and November. However, he warned that long-range forecasts involve considerable uncertainty and advised people to follow regular daily weather updates.
Meanwhile, Bangladesh received 68% less rainfall than normal in October.