DHAKA, June 4, 2026 (BSS) - Southwest monsoon may onset in first half of June over the country with possibility of 5-7 days light to moderate thunderstorms over the country this month, according to Bangladesh Meteorological Department.

"There is possibility of 5-7 days light to moderate thunderstorms over the country this month (June)," said the Long Range Weather Forecast for June 2026 issued on June 1 last.

It said rainfall is likely to be below normal all over the country. Low Pressure System is likely to form over the Bay of Bengal and one of them may intensify into a monsoon depression.

Day and night temperature is likely to be above normal over the country. Two to three mild (36-37.9øC) to moderate (38-39.9øC) heatwaves are likely to occur at isolated places over the country during this month, said the monthly climate outlook.

The country's major rivers are likely to flow normally in June. However, due to isolated heavy rainfall, the water levels of rivers in the northern, northeastern and southeastern parts of the country may increase temporarily.

A meeting of the Expert Team on Long-Range Weather Forecasting was held on 1 June 2026 at the Storm Warning Centre in Dhaka. During the meeting, various data and information for May 2026 were analysed. 
According to official data, normal rainfall (+7.4%) was recorded over Bangladesh during May 2026. Below-normal rainfall occurred in the Chattogram, Khulna, and Barishal divisions, while above-normal rainfall was observed in all other divisions. 

Moderately heavy to very heavy rainfall occurred at most places across the country during 1-4, 6, 10-13, 17-18, and 23-28 May 2026. In addition, light to moderate rainfall was observed in many areas on most days of the month, accompanied by thunderstorms, lightning, hail, gusty winds, and squally winds due to the interaction between westerly and easterly wind flows. 

The highest daily rainfall of the month was recorded at Dinajpur, measuring 144 mm on 13 May 2026, the data showed. 

A mild heatwave affected many parts of the country during 16-26 May and 29-31 May 2026 due to the presence of a thermal low over West Bengal, India, and the adjoining western region of Bangladesh. 

During the month of May, the highest maximum temperature was 38.0øC recorded at Chuadanga on 18 May 2026, while the lowest minimum temperature was 18.4øC recorded in Sylhet on 3 May 2026. 

The monthly maximum, minimum, and mean temperatures were below normal by 0.3øC, 0.5øC, and 0.4øC, respectively. Overall, the observed rainfall, temperature, heatwave conditions, Kalbaishakhi activities, thunderstorms, agro-meteorological conditions, and river conditions during May 2026 were generally consistent with the monthly forecast.