As monsoon retreats, Kerala likely to see below-normal rainfall

With the southwest monsoon starting the formal withdrawal from the country, originally from Rajasthan on September 14, three days ahead of its normal withdrawal date, the four-month rainy season in Kerala is likely to conclude with below-normal rainfall this year. The State has received a total of 1,612.6 mm of rainfall as of September 15 against the seasonal average of 1,888.2 mm of rain, a shortfall of 15%. The shortfall is likely to widen slightly as the major oceanic parameters or atmospheric conditions are not favourable for pushing the monsoon current into the State during the fag end of the season.

The tentative latitude of upcoming weather systems in the Bay of Bengal is also not very favourable for triggering any intense spells in Kerala during the next two weeks. However, light to moderate and short-lived spells are expected to continue. As per the long-period average, Kerala has to receive a normal rainfall of 2,018.7 mm during the four-month season. Although the season is expected to be below normal, the southwest monsoon will be ‘normal’ in the logbook of the Indian Meteorological Department (IMD), as a deviation of within 19% of the long-period average is considered ‘normal’ by the IMD (i.e., rain within the range of 1625.1 mm to 2412.3 mm is normal).

Though the monsoon was somewhat evenly distributed across the State this year, rain would be deficient in Idukki, Wayanad and Malappuram, where rain is already 36%, 37% and 26% deficient, respectively. Last year as well, the southwest monsoon was 13% below normal in Kerala. However, the State received a normal northeast monsoon rainfall, replenishing the water bodies. For Kerala, the withdrawal of the southwest monsoon is marked by the beginning of the northeast monsoon, with easterly winds becoming stronger up to 4.5 km above mean sea level.

This year, the evolving negative Indian Ocean Dipole (IOD) conditions, a climate driver characterised by cooler-than-normal sea surface temperature (SST) off the coast of Africa and warmer SST on the eastern side of the Indian Ocean, and the cool equatorial Pacific nearing the La Niña threshold are expected to have a strong bearing on the northeast monsoon rainfall, according to experts.