Durga Puja could be marred by rain this year if a Bay system expected to make landfall in Odisha ends up crossing Bengal. Even if it doesn’t, Calcutta is likely to see wet spells before, during, and after the festival.

The Met office, in a Puja forecast on Friday, warned of three consecutive systems forming over the Bay of Bengal over the next two weeks, one of which poses a threat to the festival week.

• The most immediate system is a cyclonic circulation currently located over the North Andaman Sea and adjoining Myanmar coast. It is expected to move slowly along the Myanmar coastline and reach the east-central and adjoining northeast Bay of Bengal by Sunday. From there, it is likely to move northwest across the Bay. Under its influence, a low-pressure area is likely to form around September 23.

• A second low-pressure system is expected to develop over the northeast Bay around September 25-26. This system carries a moderate probability of intensifying into a depression over the northwest Bay by September 27, before crossing the Odisha coast the same day and moving towards central India.

Its path will determine rainfall intensity in Bengal. If it crosses north Odisha, south Bengal — including Calcutta — is likely to experience heavy rain. If it veers towards south Odisha, the impact on Bengal will be milder, though some rainfall remains likely, forecasters said.

• The third system is a remnant of a circulation over the South China Sea, likely to emerge in the north Bay of Bengal around September 30.

This year, Sashthi falls on September 28, placing Puja in the middle of the forecast window.

“The next 10 to 12 days are likely to be rainy,” said H.R. Biswas, head of the Regional Meteorological Centre in Alipore. “Heavy rain is not ruled out during Durga Puja. If the second low-pressure hits land in north Odisha, south Bengal is likely to get heavy rain. If it hits land in south Odisha, the impact in south Bengal will be comparatively less. But some rain is almost inevitable.”

According to the Met bulletin, heavy rain is expected in Bengal’s coastal districts between September 26 and October 2, while light to moderate rain is likely across most of south Bengal, including Calcutta, during the same period. For Calcutta, light to moderate rain is “very likely” almost daily between September 21 and October 2.

This year, Puja is earlier than usual. The southwest monsoon has just begun retreating, starting its withdrawal from parts of west Rajasthan on September 14, slightly ahead of the normal September 17 schedule. The monsoon usually withdraws from Calcutta around October 10.

In recent years, Puja weather has remained unpredictable. Last year, the Met office forecast a cloudy Puja with rain and thunderstorms, but the weather stayed largely sunny and humid.

In 2023, a depression over the Bay intensified into Cyclone Hamoon, which threatened to hit Bangladesh and raised concerns in Bengal. Hamoon became a “very severe cyclonic storm” with winds over 120 kmph, but veered away, sparing Calcutta from a major washout — only a brief shower on Navami, and Dashami was dry. In 2022, a cyclonic circulation drenched Calcutta during the festival.