With Durga Puja around the corner, a fresh spell of rain looms over south Bengal, triggering worry among organisers.

A new weather system is likely to form over the Bay of Bengal around September 20, just a day before Mahalaya (September 21) and a week ahead of Sashthi (September 28), according to an extended range forecast from the Met office.

“There is a likelihood of formation of a fresh upper air cyclonic circulation or low-pressure area over west-central and adjoining northwest Bay of Bengal during the first half of week 2 (around September 20),” stated the forecast for the fortnight from September 12 to 25.

Whether or not the system brings heavy rain to south Bengal depends on its exact position. H.R. Biswas, head of the weather section at the Regional Meteorological Centre in Alipore, told Metro: “A system on the west-central Bay usually impacts south Odisha and north Andhra Pradesh more. But if it moves closer to the northwest Bay, near the Bengal coast, the likelihood of significant rain in south Bengal, including Calcutta, increases.”

Currently, a cyclonic circulation over east Bihar has triggered fresh rainfall in Bengal. This system, in combination with a trough in the westerlies, is drawing significant moisture into the state, a Met official said. North Bengal is getting more rain from the system than south Bengal.

Calcutta remained overcast on Monday. Between 8.30am and 5.30pm, the Met office recorded around 15mm of rain in Alipore.

On Tuesday, Calcutta is expected to see light rain and generally cloudy skies.

North Bengal is expected to see continued heavy rainfall, while south Bengal, including Calcutta, will likely receive light to moderate rain till Wednesday.