A low-pressure area expected to form over the Bay of Bengal over the next couple of days is likely to push the monsoon to Calcutta and other parts of south Bengal next week.

The usual date of the monsoon’s arrival in the city is June 8.

“The low-pressure system is expected to form over the central Bay of Bengal. Riding the system, the southwest monsoon is expected to reach Bengal next week,” said G.K. Das, the director of the India Meteorological Department, Calcutta.

“The system will bring the monsoon to Calcutta. Odisha will also see the onset of the monsoon during the same time. The amount of rainfall in south Bengal is dependent on the system’s proximity to the Bengal coast,” Das said.

The monsoon is declared to have arrived at a place when a large area receives frequent and widespread rain.

Calcutta might have been receiving sporadic rain, accompanied by thunderclouds and lightning, over the past few days but it was pre-monsoon rain, a weather scientist said. Thursday, too, saw a spell of wind and traces of rain.

The showers next week will bear the signs of a shift from thunderstorms to sustained rainfall that the monsoon is associated with.

The rainfall over the past few days had been accompanied by lightning and wind, typical of squalls of April and May. The monsoon reached the Andamans and Nicobar islands on May 17, five days before schedule.