A fresh system is tipped to trigger heavy rain in south Bengal over the next few days, the Met office has said.

Calcutta is most likely to get heavy rain on Sunday, according to the forecast.

“An upper air cyclonic circulation lies over southwest Bangladesh and adjoining Gangetic Bengal. It extends upto 7.6km above mean sea level.... Under its influence, a low-pressure area is likely to form over the north Bay of Bengal and adjoining coastal Bangladesh and West Bengal during the next 48 hours. Subsequently, it is likely to move slowly west-northwestwards across Gangetic West Bengal and north Odisha and Jharkhand,” said a Met bulletin issued on Saturday.

The east-west trough runs from the cyclonic circulation... to northeast Madhya Pradesh across Jharkhand, north Chhattisgarh between 3.1km and 4.5km above mean sea level, it stated.

“Under their influence, light to moderate rainfall at most places with isolated heavy to very heavy rainfall are very likely in some districts of Bengal,” the bulletin said.

This year, the monsoon set foot in south Bengal on June 17. Since then, Calcutta and most of south Bengal have been rainy. The active monsoon currents, aided by successive weather systems, have triggered the rainfall.

On Saturday, Calcutta woke up to a sharp spell of rain. The Met office recorded around 17mm of rain in Alipore between 8.30am and 5.30pm on Saturday. The conditions remained overcast throughout the day. Rain came at periodic intervals. But the showers were light.

At 28.6 degrees, the maximum temperature was four notches below normal.

On Sunday, light to moderate rain is expected across south Bengal. Heavy to very heavy rainfall (7-20cm) is likely in South 24-Parganas, East Midnapore, West Midnapore, Bankura and Jhargram. Heavy rainfall (7-11cm) is expected in Calcutta, North 24-Parganas, Hooghly,
Howrah, East Burdwan, West Burdwan and Purulia.

Thunderstorms with gusty wind (speed reaching 30-40kmph) and lightning are expected across south Bengal, according to the forecast.

On Monday, heavy to very heavy rainfall is likely in East Midnapore, West Midnapore, Jhargram, Bankura and Purulia.

Heavy rain is likely in Birbhum, East Burdwan, West Burdwan, Hooghly, Howrah and South 24-Parganas.