Kolkata: Powerful Bay systems, including depressions and low-pressure areas, kept the monsoon on track in Bengal in 2026. In Kolkata, the seasonal rain surplus was 28% and in South Bengal, the rain excess was 8%. North Bengal had a seasonal rain deficit of 13%. A deviation of plus or minus 15% is considered to be within normal range.
During this period, Kolkata recorded 1,718.9 mm rainfall against a normal of 1,345.5 mm. Overall, South Bengal logged 1,265.3 mm against the normal 1,166.8 mm. North Bengal recorded 1,647.1 mm against the normal value of 1,882.8 mm.
In meteorological parameters, June-Sept is counted as the monsoon season. Six monsoon depressions — two each in July, Aug and Sept — had formed over Bay of Bengal, with three intensifying into deep depressions. These systems ensured the monsoon current remained active on most days during the season.
The rain surplus was highest in East Midnapore at 48%, followed by West Midnapore at 40% and North 24 Parganas at 29%, according to a special monsoon report by IMD . This year, the southwest monsoon arrived in North Bengal on June 9. It then advanced over most parts of South Bengal, including Kolkata, on June 12. By June 15, it had covered all of the state. The monsoon started retreating from parts of Bengal by Oct 12 and by Oct 15, it had departed from the state completely.
“During monsoon, 101% of the long-period average (LPA) rainfall has occurred over Bengal,” the IMD special monsoon analysis report said. Monsoon’s departure is considered normal when it happens between the first and second weeks of Oct.
Systems like these are important during the monsoon for sufficient rain,” said H R Biswas, head at Regional Meteorological Centre, Kolkata. “Five out of these six depressions had an impact in the rain intensity and frequency in Bengal.