A strong El Nino developing over the Pacific Ocean has put Tamil Nadu's upcoming Northeast Monsoon under close watch. While El Niño is often associated with weaker rainfall during India's Southwest Monsoon, its impact on Tamil Nadu's October–December rainfall can be very different.
What is happening now?
Sea surface temperatures in the central and eastern equatorial Pacific have risen significantly, indicating strong El Niño conditions. The Niño 3.4 index, one of the key indicators used to monitor El Niño, has strengthened considerably, and some climate models indicate that the event could intensify further in the coming months.
The El Niño conditions are also expected to continue into 2027.
Does El Niño mean less rain for Tamil Nadu?
Not necessarily.
Tamil Nadu receives a major share of its annual rainfall from the Northeast Monsoon between October and December. Historical records show that several El Niño years have actually produced good or even excessive Northeast Monsoon rainfall in the State.
For example, Tamil Nadu experienced strong Northeast Monsoon seasons during El Niño years such as 1997, 2015 and 2023.
However, the relationship is not guaranteed. There have also been El Niño years when Tamil Nadu received poor rainfall.
This means El Niño alone cannot be used to predict whether the State will face floods or drought.
Why is 2015 important?
The 2015 El Niño period is an important example of how extreme the situation can become.
Chennai experienced exceptionally heavy rainfall and severe flooding during November and December 2015. Between November 1 and December 5 that year, Chennai received around 1,416.8 mm of rain, compared with a normal of about 408.4 mm for the period.
But the following Northeast Monsoon season in 2016 turned sharply in the opposite direction, with Tamil Nadu recording a major rainfall deficit.
It demonstrates how dramatically rainfall can vary even around an El Niño period.
Could Tamil Nadu receive more cyclones?
El Niño can influence the formation, intensity and movement of weather systems and cyclones, but it is only one factor.
The eventual Northeast Monsoon will also depend on conditions over the Bay of Bengal and Indian Ocean, including sea-surface temperatures, the Indian Ocean Dipole (IOD), the Madden-Julian Oscillation (MJO) and the number and tracks of low-pressure systems.
These factors can determine whether moisture-bearing systems move towards the Tamil Nadu coast or elsewhere.
What should Tamil Nadu prepare for?
The bigger concern is therefore not simply whether rainfall will be "above normal" or "below normal".
A strong El Niño combined with unusually warm oceans could increase the possibility of extreme and highly variable weather — including intense rainfall over short periods, urban flooding, longer dry spells, water shortages and unusually high temperatures.
Tamil Nadu's expert advisory committee has consequently recommended preparing for multiple hazards rather than treating El Niño only as a drought signal.
The key takeaway
El Niño does not automatically mean drought for Tamil Nadu.
Historically, strong El Niño years have sometimes brought substantial Northeast Monsoon rainfall to the State. But El Niño is only one part of a much more complex weather system.
As Tamil Nadu approaches its crucial October–December rainy season, the important factor will be how El Niño interacts with the Bay of Bengal, Indian Ocean conditions and developing weather systems.
For Tamil Nadu, the coming Northeast Monsoon therefore needs to be watched not just for the total amount of rainfall but also for where, when and how intensely that rain falls.
