A low-pressure area has formed over North Bay and adjoining area, according to Bangladesh Meteorological Department (BMD).
The axis of monsoon troughs runs through Uttar Pradesh, Bihar, West Bengal, center of the low to Assam across southern part of Bangladesh, it said.
Monsoon is fairly active over Bangladesh and moderate over North Bay.
Another low pressure area may form over east central Bay and adjoining North Bay on September 24 and it is likely to intensify, it added.
The Met office also predicted light to moderate rain/thunder showers accompanied by temporary gusty wind at many places over Khulna, Barishal & Chattogram divisions and at a few places over Rangpur, Rajshahi, Mymensingh, Dhaka & Sylhet divisions with moderately heavy to heavy falls at places over Khulna, Barishal & Chattogram divisions.
Day and night temperature may fall slightly over the country.