The maritime ports of Chittagong, Cox's Bazar, Mongla, and Payra have been advised to hoist local cautionary signal number 3 as strong monsoon persists over the North Bay.
A deep convection is taking place under its influence.
Squally weather may affect the maritime ports, North Bay and adjoining coastal areas of Bangladesh, the Met Office said.
All fishing boats and trawlers over the North Bay have been advised to remain close to the coast and proceed with caution until further notice.
They are also advised not to venture into the deep sea.
According to the regular weather forecast, light to moderate rain or thundershowers is likely to occur at most places over Rangpur, Mymensingh, and Sylhet divisions and at many places over Dhaka, Khulna, Barisal, Rajshahi, and Chittagong divisions.
Some places can see moderately heavy to heavy falls, the Met Office said in a 24-hour forecast commencing 6am on Friday.
The axis of monsoon trough runs through Rajasthan, Uttar Pradesh, Bihar, West Bengal to Assam across the central part of Bangladesh. One of its associated troughs extends up to the North Bay.
Monsoon is active over Bangladesh and moderate to strong over the North Bay, the weather office said.
Day and night temperature may remain nearly unchanged all over the country.