El Nino Weakening: Above-normal rainfall forecast this monsoon

New Delhi: The India Meteorological Department has forecast above-normal rainfall during the upcoming June-September southwest monsoon season. The seasonal rainfall forecast is expected to be 106 per cent of the long-period average (LPA), which is 870 mm (1970-2020 average).

This is the first time in a decade the IMD has predicted above-normal rainfall, that too in its first-stage long-range forecast, which is issued nearly 45 days in advance of the actual onset of the southwest monsoon over Kerala on June 1 (see table). The IMD categorises the seasonal rainfall as above-normal when it ranges between 105-110 per cent of the LPA.

“The country can expect good monsoon rainfall during the southwest monsoon season this year. The seasonal rainfall will be 106 per cent of the LPA,” said IMD Director-General Mrutyunjay Mohapatra. He was speaking in New Delhi on Monday during the release of the first-stage long-range forecast for the southwest monsoon season in 2024.

There are multiple favourable factors indicating a high probability for above-normal rainfall during the June-September period this year, according to the sources at the Ministry of Earth Sciences. Of these, the vital oceanic factor is the El Nino, an event associated with the above-normal sea-surface temperatures prevailing over the equatorial Pacific Ocean.

It is known to cause extreme heatwaves and suppress the Indian summer monsoon rainfall.

The ongoing El Nino event, the IMD said, is weakening. “But it continues to remain in the ‘moderate’ category. Closer to the onset of the southwest monsoon season, El Nino Southern Oscillation neutral conditions are likely to establish,” said Mohapatra.

“Thereafter, La Nina conditions are expected to emerge during the second half of the monsoon season, which could bring higher-than-normal rainfall over the country,” he added.

In a study, the IMD noted that during a La Nina year following an El Nino event (like 2024), the southwest monsoon rainfall had in the past remained normal or above (nine occasions during 1951-2023). “But there are many other ocean-atmospheric dynamic factors which affect rainfall during the monsoon season apart from La Nina, which we do not have good knowledge of yet,” he said.