El Nino conditions likely to persist through March 2027 impacting Chennai weather

The Indian National Centre for Ocean Information Services (INCOIS) has forecast that El Nino conditions in the central and eastern equatorial Pacific Ocean are likely to persist with up to a 98 percent probability through March 2027, bringing significant weather implications for Chennai and Tamil Nadu.

The weather phenomenon, which became established in June, is projected to remain the dominant phase through the southwest monsoon, the northeast monsoon, and the winter. The World Meteorological Organization (WMO) has also projected a rapid development into a strong El Nino.

This persistent El Nino poses a dual impact for Chennai. Historically, the phenomenon weakens the southwest monsoon by reducing moisture transport from the Arabian Sea, leading to dry spells and prolonged heatwaves. Already, a weak southwest monsoon has coincided with hot, humid weather along the coast and prolonged heatwave conditions over the interior regions of Tamil Nadu.

According to historical rainfall data, Chennai has recorded below-normal June-to-September rainfall in eight of the nine El Nino years since 1987, compared to its seasonal average of 44 centimeters.

However, El Nino historically favors a wetter northeast monsoon over Tamil Nadu by creating conditions conducive to rain-bearing systems over the Bay of Bengal. The northeast monsoon accounts for nearly 60 percent of Chennai’s annual rainfall and about 48 percent of Tamil Nadu’s yearly total. Weather blogger Pradeep John noted that strong El Nino years such as 1997, 2015, and 2023 brought excess northeast monsoon rainfall over Chennai and much of the state, though the final outcome still depends on other climate drivers like the Indian Ocean Dipole.

Beyond rainfall, INCOIS warned that persistent El Nino conditions could intensify marine heatwaves, trigger coral bleaching, and affect fisheries by altering marine ecosystems in the northern Indian Ocean.

In the short term, the India Meteorological Department (IMD) has forecast light to moderate rain accompanied by thunderstorms over Chennai and neighbouring districts on Friday evening or night, bringing temporary relief from maximum temperatures of around 37 to 38 degrees Celsius.