THIRUVANANTHAPURAM: After days of speculation over its delayed arrival and uncertainty over its onset, the southwest monsoon is likely to set in over Kerala on Thursday. The India Meteorological Department (IMD) said that conditions have become favourable for the onset of the southwest monsoon over Kerala within the next 24 hours, while forecasting heavy to very heavy rainfall across the state over the coming week.
In 2025, Kerala received a total rainfall of 1,752.7 mm against a normal rainfall of 2,018.6mm recording a deficit of 13%. The forecast comes amid questions over the delayed and frequently revised monsoon onset dates this year. However, weather experts say the uncertainty is linked to the complex interplay of several atmospheric systems that govern monsoon progression.
Cusat Advanced Centre for Atmospheric Radar Research director S Abhilash said that the monsoon’s arrival does not occur on the same date every year and depends on the strength of supporting systems over the Indian Ocean and the Pacific region.
“The technical criteria required for monsoon onset, including rainfall, cloud cover and wind patterns, are being satisfied. Therefore, it can be declared as the onset of the monsoon. However, this is likely to be a weak onset because several supporting systems are absent or weak,” he said.
He said that the Madden-Julian Oscillation, a key atmospheric phenomenon that enhances monsoon activity, is currently weak. In addition, there are no significant low-pressure systems over the Bay of Bengal or the western Pacific that would normally help strengthen and pull the monsoon flow towards the Indian mainland.
“The monsoon winds have reached the region, but there is insufficient force to intensify them. The onset may happen at any time, but its intensity is expected to remain weak initially,” said Abhilash.
According to the IMD, a cyclonic circulation currently persists over the Karnataka coast and adjoining east-central Arabian Sea, and these systems are expected to aid rainfall activity over Kerala. On the evolving El Nino conditions in the Pacific Ocean, Abhilash said there is no indication of a Super El Nino at present, though El Nino appears to be developing earlier than expected.
“In an El Nino year, rainfall over mainland India is generally expected to be below normal because weather systems that generate widespread rain form less frequently,” he explained. He said that though seasonal rainfall may be below normal, intense rain spells are still likely.