Why is the monsoon early this year?

The Monsoon’s Early Arrival

• The onset date for the southwest monsoon over Kerala is around June 1, a week ahead of its normal onset.

• Early arrival is celebrated but doesn’t always guarantee a bountiful monsoon.

• Late arrival by more than two weeks often brings a deficit.

The Science of the Monsoon Onset

• There are many theories about the science of the onset, but there is no consensus on a complete understanding of the processes leading to the onset.

• The onset has been systematically delayed by a few days since the 1970s.

• The impact of global warming on the regime shift poses further barriers to understanding and predicting shifts in the onset.

Previous and Present Early Onsets

• This year’s onset was the earliest in 16 years; the last was on May 23, 2009.

• External factors such as more cyclones occurring late into the pre-monsoon cyclone season, global warming, and an unusual sea surface temperature anomaly pattern in the tropical Pacific have played a role in the onset.

The Monsoon’s Arrival to Kerala

• More cyclones are occurring late into the pre-monsoon cyclone season, some have pulled the trough forward to deliver an early onset.

• The northward pull on the western end of the trough indicates that the low-pressure system trudging along the west coast may have played a role in the earliness.

• Typhoons in the Pacific have also pulled moisture away from the Indian Ocean during the onset phase to delay the onset.

The Future of the Monsoon

• The forecasts call for a neutral year for the El Niño and the Indian Ocean Dipole, which would make 2025 different from 2009.

• Some decadal climate variability indicators are favoring an El Niño to evolve this summer.

Changing Seasonal Rainfall Distribution

• There are no clear answers as to the causes of the monsoon’s early onset this year or any year.

• The merger of the southwest monsoon with the northeast monsoon in some regions of the country and erratic rainfall distribution within the season remain a challenge.