The Bay system intensified into a depression before hitting land in north Odisha on Sunday afternoon, the Met office said.

Calcutta saw a consistently cloudy sky and intermittent rain between Sunday morning and night. Met officials said clouds trailing the system may still trigger significant rainfall in and around the city. However, the intensity and spread of showers are expected to gradually reduce across south Bengal over the week, while north Bengal is likely to see a renewed spell of heavy rain, according to the forecast.

The Bay system, a well-marked low-pressure area on Saturday morning, had intensified into a depression by Sunday morning, said the Met office. It struck land near Balasore in coastal Odisha, more than 240km from Calcutta.

“The depression over northwest Bay of Bengal and adjoining areas of north Odisha-West Bengal coasts moved west-northwestwards... crossed north Odisha coast close to Balasore around 2.30pm. It lay centred at 5.30pm over coastal areas of north Odisha and adjoining West Bengal, about 50km west-northwest of Balasore (Odisha), 50km southwest of Baripada (Odisha), 100km east of Keonjhargarh (Odisha) and 140km south-southeast of Jamshedpur (Jharkhand),” said a Met bulletin issued on Sunday night.

“It is very likely to move nearly west–northwestwards across north Odisha and adjoining south Jharkhand and north Chhattisgarh during the next 24 hours,” the bulletin said.

A sting in the tail of Bay systems has translated to heavy rain in Calcutta more than once in recent years.

A Met official said Odisha was southwest of the system, when it was over the Bay,
and south Bengal was northeast of it.

“The areas on the south of a Bay system bear the maximum impact. This system had more impact in Odisha than in Bengal. Coastal areas like East Midnapore, which share a border with Odisha, got more rain than North and South 24-Parganas and Calcutta,” said the official.

The Met office recorded less than 10mm of rain in Alipore till 8.30pm on Sunday. The maximum temperature was 30 degrees, two and a half notches below what is normal for early July.

On Monday, heavy rain is likely in Purulia, West Burdwan and Birbhum districts. Thunderstorm activities are expected in the remaining districts.

The intensity of the rainfall will decrease in South Bengal from Tuesday. “The sky will take turns remaining sunny and cloudy. Some moisture will remain, and enough heat may lead to localised thunderstorm activities,” said the Met official.

The volume and intensity of the rain will rise in north Bengal from Tuesday.