The Lift Line
“If we monitor the ocean consistently, we can also spot these events early.” (R. Venkatesan, The Hindu)
Why This Explainer Matters
This signed column on The Hindu’s Science page, in the print edition of 11 October 2026, is by R. Venkatesan, former consultant with UNESCO IOC, Paris, and adjunct professor at the University of Massachusetts, Dartmouth. It takes up a question every aspirant meets in geography: if El Niño usually means a weak monsoon and drought for India, why can Tamil Nadu see heavy rain in an El Niño year? The answer lies in the northeast monsoon, which gives the state its main rainy season, about 48% of its annual rain, between October and December.
This explainer reads the column alongside the India Meteorological Department’s (IMD) outlook for the 2026 northeast monsoon and NOAA’s latest El Niño discussion, so that you can separate the official forecast from the author’s own reasoning. For the southwest monsoon that has just ended, see our report on the 2026 monsoon ending at 87% of normal; for El Niño’s ecological effects, see our editorial on El Niño and the monitoring of ecological stress. This piece adds what those did not cover: the northeast monsoon, the Indian Ocean Dipole, and Tamil Nadu’s different response.
GS Paper 1: Important geophysical phenomena; salient features of the world’s physical geography (monsoons, ENSO, the Indian Ocean Dipole). GS Paper 3: Disaster and disaster management; irrigation and water use in agriculture.
In the news: with a strong El Niño under way in the Pacific, IMD expects normal northeast monsoon rain over South Peninsular India, and normal to above-normal rain in southern parts of Tamil Nadu and Kerala.
New to this topic? Start here: the basics in plain words (revision card 1 of 7)
Background and Context
What El Niño is
The El Niño Southern Oscillation (ENSO) is a climate pattern of the tropical Pacific whose effects are felt worldwide. The basics, as NOAA’s Climate Prediction Center sets them out:
| Point | What NOAA says |
|---|---|
| Where | El Niño is monitored in the east-central equatorial Pacific; the name “originally referred to an annual warming of sea-surface temperatures along the west coast of tropical South America” |
| When it is declared | When the three-month average sea-surface temperature departure exceeds 0.5°C in the east-central equatorial Pacific |
| How often | Episodes “typically occur every 3-5 years”, though the interval has varied from 2 to 7 years |
The column describes 0.5°C as the typical warming. In NOAA’s definition it is the threshold at which an El Niño is declared.
How strong this year’s El Niño is
| Agency | What it says |
|---|---|
| IMD (northeast monsoon outlook) | “Strong El Niño conditions are currently prevailing over the equatorial Pacific Ocean”; models indicate it “will continue to strengthen through the end of the year” and is likely to continue early next year |
| NOAA Climate Prediction Center | Status: El Niño Advisory; “a strong-to-very strong El Niño likely through January-March 2027 (remaining greater than an 83% chance)”; the Niño-3.4 index has reached +2.1°C |
The northeast monsoon
IMD explains the season this way: the return of the north-easterly trade winds over South Asia, “associated with the southward movement of the Intertropical Convergence Zone (ITCZ)”, brings rain to the extreme south of India, Sri Lanka, the Maldives and the southern coast of Myanmar.
| Fact | IMD |
|---|---|
| Season | October to December (OND) |
| South Peninsula’s share of annual rain | About 30% |
| Tamil Nadu’s share | About 48% |
| Why it matters for farms | The season “coincides with the second major agricultural season” |
| IMD’s seasonal forecasts for it | Issued since 1998 |
IMD director Mrutyunjay Mohapatra told reporters in Chennai that the northeast monsoon is likely to set in over Tamil Nadu between 15 and 21 October.
The Indian Ocean Dipole (IOD)
The Indian Ocean has its own climate driver. Japan’s research agency JAMSTEC measures it with the Dipole Mode Index (DMI): the sea-surface temperature gradient between the western equatorial Indian Ocean (50°E-70°E, 10°S-10°N) and the south-eastern equatorial Indian Ocean (90°E-110°E, 10°S-0°). When the index is positive, the event is a positive IOD; as the column puts it, the western ocean near Africa is then warmer than the eastern ocean near Indonesia.
IMD says neutral IOD conditions prevail now and are likely to continue through the northeast monsoon season.
IMD’s outlook for October to December 2026
| Region or variable | Outlook |
|---|---|
| South Peninsular India, season total | Normal: 88-112% of the Long Period Average (LPA). The LPA, based on 1971-2020 data, is about 334.13 mm |
| Southern parts of Kerala and Tamil Nadu | Normal to above-normal |
| Most of the remaining region | Below normal |
| October 2026 | Normal to above normal in many areas of south Tamil Nadu, some areas of north Tamil Nadu and the hilly areas of Kerala; below normal in most of the rest |
| Temperatures | Above-normal maximum and minimum temperatures over most of the region |
IMD prepared the outlook with its Multi-Model Ensemble, which includes its own Monsoon Mission Climate Forecast System (MMCFS). It released it at a forum held with the Tamil Nadu Disaster Risk Reduction Agency (TNDRRA) and the National Institute of Ocean Technology (NIOT).
The Analysis
1. The all-India rule does not travel south. In an El Niño year, writes R. Venkatesan in The Hindu, India “has recorded deficient rainfall and a higher incidence of droughts, on average. However, Tamil Nadu has reported a strikingly different pattern.” The long record supports him: a study of coastal Tamil Nadu from 1901 to 2020, published in IMD’s journal Mausam, concluded that “prolonged El Niño events lead to excess rainfall, while La Niña events result in rainfall deficit.” The IMD director made a milder point: El Niño “generally did not have a major negative impact on Northeast monsoon rainfall”, though “the relationship between El Nino and rainfall had changed over time.”
2. Why the difference, in the author’s account. The column cites studies that give two reasons. First, in strong El Niño years, pressure differences between the Bay of Bengal and the Arabian Sea create what it calls a “wind tunnel” effect that “drives moist air into coastal Tamil Nadu”. Second, when El Niño coincides with warmer waters in the Bay, evaporation increases; cyclonic circulations in November and December then release the stored heat as intense, localised rain. For October to December 2026, it adds, El Niño “can strengthen moisture inflow from the Bay of Bengal”. He adds that in El Niño years winds weaken and skies clear, letting more sunlight heat the ocean, while the Bay’s shallow mixed layer and salinity stratification trap that heat. These are the column’s explanations, credited to unnamed studies; IMD’s outlook names ENSO as a major influence on the season’s year-to-year variability but does not set out a mechanism.
3. Cyclones: fewer, but they can still come ashore. The column says such years have “often resulted in frequent and heavy rains and cyclones along the Tamil Nadu coast.” The IMD director drew a finer line: in an El Niño year “the number of cyclones formed is likely to be lower”, but cyclones forming over the southern or south-eastern Bay of Bengal and moving west-northwest “could increase the possibility of cyclones moving towards the coastal areas of Tamil Nadu, Puducherry, southern Andhra Pradesh and Sri Lanka.” Fewer storms do not mean less danger for the Tamil Nadu coast.
4. The 2015 lesson, read with care. The column recalls the 2015 Chennai floods: India as a whole faced a weak southwest monsoon that year, it notes, while Tamil Nadu was hit by devastating floods. The World Weather Attribution study of the 1 December 2015 downpour found that some stations recorded as much as 494 mm in 24 hours, the region’s heaviest one-day rainfall in more than a century, and that “The 2015 rainy season coincided with a strong El Niño”. But it also found that “In the observations, the ENSO signal is also present but not statistically significant.” A strong El Niño can raise the odds of an extreme spell; a single flood cannot be pinned on it.
5. A forecast is a probability, not a promise. The column notes that forecasts are updated when a depression or cyclone develops, because a cyclone’s formation is nonlinear and hard to predict until it has fully developed. IMD makes a similar point about the whole season: its predictability is “limited to some extent by the strong day to day atmospheric variability”, caused by disturbances in the tropical easterlies and the Madden-Julian Oscillation (MJO). IMD’s outlook is a set of probabilities for three categories (above normal, normal, below normal), not a rainfall total for each district.
6. The ask: watch the ocean. The author’s remedy is observation. Satellites measure sea-surface temperature, rainfall and trade winds; buoys, boats, deep-water stations and coastal radars add data below and beside them, and together they give “a 3D picture of how the ocean and the atmosphere are changing.” Consistent monitoring, he argues, would let us “spot these events early”. He calls the ocean one of the least observed parts of the earth system.
Data and Institutions Vault
Prelims-grade facts:
- El Niño threshold (NOAA): three-month average sea-surface temperature departure above 0.5°C in the east-central equatorial Pacific.
- ENSO cadence (NOAA): episodes typically every 3 to 5 years; the interval has varied from 2 to 7 years.
- Current strength: strong El Niño (IMD); strong-to-very strong likely through January-March 2027 (NOAA); Niño-3.4 index at +2.1°C.
- Indian Ocean Dipole: measured by the Dipole Mode Index; positive when the western equatorial Indian Ocean is warmer than the south-eastern.
- IOD this season: neutral, likely to stay neutral through the northeast monsoon (IMD).
- Northeast monsoon: October to December; the north-easterly trade winds return as the ITCZ moves south.
- Share of annual rain: about 30% for the South Peninsula, about 48% for Tamil Nadu.
- IMD outlook for the season: South Peninsula normal, at 88-112% of an LPA of about 334.13 mm (1971-2020).
- Season forecasts: IMD has issued northeast monsoon outlooks since 1998.
⚠️ Watch the trap: IMD’s normal to above-normal forecast covers only the southern parts of Tamil Nadu and Kerala (and, for October, some areas of north Tamil Nadu); most of the rest of the South Peninsula is likely to get below-normal rain. 0.5°C is the threshold for declaring an El Niño, not its usual size. And an El Niño year is likely to see fewer cyclones, not more, though their tracks can still favour the Tamil Nadu coast.
The Debate
| The column’s case | The cautions |
|---|---|
| Tamil Nadu’s El Niño years differ from India’s: a century of coastal data links prolonged El Niño events to excess rain | IMD expects below-normal rain over most of the remaining South Peninsula, so “El Niño means rain in the south” is not a rule |
| A warmer Bay of Bengal feeds evaporation and can intensify depressions | The mechanisms in the column are the author’s account; IMD’s outlook names no single mechanism |
| 2015 shows how extreme an El Niño year can turn for Chennai | The attribution study found the ENSO signal in the observations not statistically significant |
| Heavy rains and cyclones can strike the Tamil Nadu coast | The IMD director expects fewer cyclones in an El Niño year, though some may track towards the coast |
| Better ocean observation means earlier warning | Seasonal predictability is limited by day-to-day atmospheric variability, so observation improves warnings but cannot remove surprise |
How to Think About This
Treat El Niño as a global driver with regional outcomes. The same Pacific warming that weakens the southwest monsoon over most of India can arrive in Tamil Nadu through a different door, the October to December northeast monsoon. When you write about ENSO in a Mains answer, name the season and the region before naming the effect.
Then read the forecast the way IMD writes it: a probability by area, not a promise for the state. A normal season total for the South Peninsula can hide heavy rain in the south and a shortfall elsewhere. IMD’s own advice is to act early: use its impact-based forecasts and risk-based advisories, and, for the areas likely to fall short, promote water conservation, efficient irrigation and agricultural contingency measures.
Diagram-in-Words
One El Niño, two Indias
Why a strong Pacific warming can mean a different season for Tamil Nadu.
Takeaway Box
- The argument: an El Niño year that brings India drought on average can bring Tamil Nadu heavy rain, because the state’s main rain comes from the northeast monsoon.
- This year: a strong El Niño (IMD), strong-to-very strong through January-March 2027 (NOAA), with a neutral Indian Ocean Dipole.
- The outlook: a normal season for the South Peninsula (88-112% of LPA); normal to above-normal in the southern parts of Kerala and Tamil Nadu; below normal over most of the rest.
- The caution: fewer cyclones are likely in an El Niño year, and the 2015 Chennai floods could not be pinned on El Niño with statistical confidence.
- The ask: watch the ocean consistently, so that these events are spotted early.
Revision Cards
UjiyariThe northeast monsoon and the dipole: card 3 →UjiyariCyclones and the 2015 lesson: card 4 →UjiyariTest yourself on card 5 →Show answer
Show answer
Show answer
UjiyariOn card 6: traps, recall and memory hooks →R1What share of Tamil Nadu's annual rain falls from October to December?
R2Since when has IMD issued northeast monsoon outlooks?
R3What is the South Peninsula's October to December LPA?
R4How often do El Niño episodes typically occur?
UjiyariWrite the Mains answer on card 7 →UjiyariNow take today’s quiz →Sources: The Hindu, R. Venkatesan, “T.N. may encounter El Nino differently from rest of India”; IMD, Forecast Outlook for the 2026 Northeast Monsoon Season; NOAA Climate Prediction Center, ENSO Diagnostic Discussion; NOAA Climate Prediction Center, ENSO FAQ; JAMSTEC, Dipole Mode Index; Mausam (IMD journal), Lakshmi et al., “Influence of sunspot activity and EL Niño southern oscillation on northeast monsoon rainfall in the coastal districts of Tamil Nadu”; World Weather Attribution, Chennai floods, December 2015; DT Next, Northeast monsoon may begin between October 15-21: IMD
Source: El Niño and Tamil Nadu: Why the Northeast Monsoon Differs — Ujiyari.com | Free UPSC & State PCS Editorial Analysis
