Strong El Nino Builds as Tamil Nadu Eyes Northeast Monsoon
A strengthening El Nino is being watched closely as Tamil Nadu awaits its northeast monsoon, which supplies most of the state's annual rainfall.
El Nino, the periodic warming of the central and eastern equatorial Pacific Ocean, has strengthened into one of the most closely tracked climate signals of the year. With the southwest monsoon retreating and leaving rainfall deficits in parts of India, attention has shifted to what the phenomenon may mean for the northeast monsoon over the southern peninsula, Tamil Nadu included.
A strong Pacific signal
Sea surface temperatures across the central-eastern equatorial Pacific remain well above average and are still climbing. Models from several countries, including the Australian government's Bureau of Meteorology, show both oceanic and atmospheric indicators aligning with a strong El Nino. The widely used Nino 3.4 index, which tracks temperature anomalies in that region, has risen to an average of +2.51 degrees Celsius, far above the +0.80 degree Celsius El Nino threshold. Some models suggest it could peak above +3.0 degrees Celsius in the months ahead.
The current episode, which began developing earlier this year, is expected to persist until around May or June 2027. El Nino events typically recur every two to seven years.
Global backdrop
The World Meteorological Organisation has cautioned that a very strong El Nino can sharply alter rainfall and temperature patterns worldwide and drive extreme weather. Its regional effects, however, vary by geography and season, and can be modified by other climate drivers such as the Indian Ocean Dipole and conditions in the Indian and Atlantic Oceans.
The event is unfolding against a rapidly warming climate. 2024 was the warmest year on record, with global temperatures crossing the 1.5 degree Celsius threshold set by the Paris agreement; 2023 and 2025 also rank among the warmest years. With the Pacific expected to warm further and El Nino conditions forecast to peak in winter and continue into next year, 2026-2027 could exceed earlier records, and the 2023-2027 span could become the warmest five-year period historically. Sivananda Damodara Pai, Head of the Regional Meteorological Centre in Chennai, noted that the strong 1997 El Nino has focused attention on the current event and its implications for the country and the seasons ahead.
What it could mean for Tamil Nadu
A strong El Nino is generally regarded as favourable for a wetter northeast monsoon over the southern peninsula. It can also alter the tracks, frequency and intensity of cyclones across ocean basins and shift monsoon patterns globally. This year it contributed to a southwest monsoon rainfall deficit in India, Tamil Nadu included.
El Nino years are usually associated with fewer weather systems forming over the Bay of Bengal, many of them weaker, with most tracking westwards towards the Tamil Nadu-Andhra Pradesh coast. Pai cautioned that El Nino is not the sole driver of extremes such as prolonged dry spells or urban flooding; rising global temperatures and climate change amplified by urbanisation and changes in land use and land cover can intensify its effects.
Meteorologists point to past records linking several El Nino years with above-normal October-December rainfall in Tamil Nadu. Y.E.A. Raj, former deputy director general of meteorology at the RMC, said the northeast monsoon was exceptionally good in 1997, 2009, 2015 — when Chennai experienced floods — and 2023, all El Nino years. But 2002 was an exception, with poor northeast monsoon rainfall despite El Nino. Several non-El Nino years, including 2005, 2010, 2011 and 2021, also recorded above-normal monsoon rainfall. A strong El Nino is a favourable factor for a good northeast monsoon, Raj said, but not a necessary condition; in 1982, an El Nino year, both the southwest and northeast monsoons failed over India.
Meteorologists note that the northeast monsoon is inherently volatile and that El Nino is only one of several parameters shaping it, with performance depending on other oceanic and atmospheric conditions.
Why the coming season matters
The northeast monsoon, active from October to December over Tamil Nadu, accounts for a major share of the state's annual rainfall. With the southwest monsoon likely to end with a deficit, the coming season is important for bridging the shortfall and replenishing depleted water resources. While meteorologists suggest El Nino and a negative Southern Oscillation Index may favour a wetter northeast monsoon, the India Meteorological Department is expected to issue its seasonal forecast towards the end of September.
The Tamil Nadu government has set up an Expert Advisory Committee to monitor and assess the potential impact of a strong El Nino and advise on preparedness and mitigation. The IMD and the Tamil Nadu Disaster Risk Reduction Agency plan to hold a northeast monsoon seasonal outlook forum on October 1.