2025-2026 ENSO Cycle and Monsoon Progression: UPSC Current Affairs Story Arc

Overview

This arc tracks the volatile transition of the El Niño-Southern Oscillation (ENSO) and its direct impact on India's 2025 monsoon. Starting with a 'Neutral' phase in April 2025, the India Meteorological Department (IMD) predicted an above-normal monsoon (105% of the Long Period Average). The monsoon arrived early, bolstered by the Madden-Julian Oscillation (MJO) and a strong Somali Jet. By late 2025, the cycle dipped into a cooling La Niña phase, which persisted through winter. However, by February 2026, the IMD issued early warnings of a potential return to El Niño, signaling a possible reversal of fortunes for Indian agriculture and water security in the subsequent year.

How This Story Evolved

Neutral ENSO forecast (Apr 2025) → Enabled above-normal monsoon prediction & early onset (May 2025) → Shift to La Niña (Sept-Nov 2025) → Forecast of El Niño return (Feb 2026)

1. 2025-04-01: IMD Predicts Warmer Summer
   More details

   UPSC Angle: IMD predicts warmer summer, rules out El Nino for southwest monsoon.

   Key Facts:

   • Organization: India Meteorological Department (IMD)
   • Prediction: Warmer summer
   • Monsoon: El Nino unlikely
2. 2025-04-12: El Niño-Southern Oscillation (ENSO) Forecast
   More details

   UPSC Angle: NOAA forecasts neutral ENSO conditions until October 2025.

   Key Facts:

   • Neutral conditions in the Pacific Ocean are expected until October 2025.
3. 2025-04-16: IMD Predicts Above-Normal Monsoon
   More details

   UPSC Angle: IMD predicts above-normal monsoon, forecasting 105% of normal rainfall.

   Key Facts:

   • IMD predicts: Above-normal monsoon.
   • Rainfall forecast: 105% of normal.
   • Season: June-September.
4. 2025-05-08: Early Onset of Southwest Monsoon
   More details

   UPSC Angle: Not exam-relevant

   Key Facts:

   • Normal date for monsoon onset over the South Andaman Sea: anytime after mid-May, normally May 19.
   • Normal date for monsoon onset over Kerala: June 1.
5. 2025-05-28: Early Monsoon Onset Triggered by Madden-Julian Oscillation (MJO)
   More details

   UPSC Angle: Early monsoon onset triggered by Madden-Julian Oscillation (MJO).

   Key Facts:

   • Mascarene High intensification.
   • Convection surge.
   • Somali Jet strengthening.
   • Heat low formation.
   • Early monsoon onset in Kerala and Mumbai triggered by Madden-Julian Oscillation (MJO).
   • MJO is a moving system of winds, clouds, and pressure.
   • MJO circles the globe typically every 30–60 days.
   • Other contributing factors: Mascarene High intensification, convection surge, and Somali Jet strengthening.
6. 2025-07-01: India to get above-normal rain in July, forecasts IMD
   More details

   UPSC Angle: IMD forecasts above-normal rainfall in India for July.

   Key Facts:

   • India
   • above-normal rain
   • July
   • IMD
7. 2025-09-02: UN Warns La Niña Return Won't Stop Global Temperature Rise
   More details

   UPSC Angle: La Niña won't stop global temperature rise, says UN.

   Key Facts:

   • La Niña could be back
   • 55% likelihood of cooling sea temperatures in the equatorial Pacific
8. 2025-11-03: India Meteorological Department forecasts mixed weather
   More details

   UPSC Angle: Not exam-relevant

   Key Facts:

   • A fresh western disturbance is set to influence northwest India from the night of November 3, 2025.
   • Light to moderate rainfall and snowfall is expected over the western Himalayan region between November 3 and 5, 2025.
   • States like Himachal Pradesh and Uttarakhand will be affected.
   • Thunderstorms are likely over the Andaman Islands and western Madhya Pradesh by November 3, 2025.
   • La Nia conditions are likely to persist from November to December 2025.
   • Negative IOD conditions are expected to weaken in the coming months.
9. 2026-02-02: El Nino Phenomenon
   More details

   UPSC Angle: El Nino phenomenon may occur after July this year.

   Key Facts:

   • El Nino phenomenon may occur after July 2026
   • Clarity will emerge in April
   • In India, El Niño causes weak rainfall and more heat

Genesis

Trigger

On April 1, 2025, the IMD officially ruled out El Niño for the upcoming monsoon, setting the stage for an 'above-normal' rainfall forecast.

Why Now

The transition from a previous cycle into a 'Neutral' phase by April 2025 removed the suppressing effect of El Niño, allowing local factors like the Mascarene High and Somali Jet to dominate.

Historical Context

Historically, years following an El Niño often transition through a neutral phase to La Niña, a pattern that typically brings beneficial rains to India but poses flood risks.

Key Turning Points

1. [2025-05-28] MJO-triggered early onset in Kerala and Mumbai

   It accelerated the monsoon progression, leading to record-breaking May rainfall in Mumbai.

   Before this: Anticipation of normal onset (June 1). After this: Accelerated advance and immediate flood management concerns.

2. [2025-09-02] WMO confirms 55% likelihood of La Niña return

   Shifted the focus from monsoon performance to potential winter rainfall and cooler temperatures.

   Before this: Neutral Pacific conditions. After this: Expectations of a persistent La Niña through late 2025.

Key Actors and Institutions

Key Institutions

• India Meteorological Department (IMD)
• National Oceanic and Atmospheric Administration (NOAA)
• World Meteorological Organization (WMO)

Key Concepts

Madden-Julian Oscillation (MJO)

An eastward-moving 'pulse' of clouds, rainfall, and winds in the tropical atmosphere that can enhance or suppress monsoon currents.

Current Fact: On May 28, 2025, the MJO was cited as the primary trigger for the early monsoon onset in Kerala and Mumbai.

Long Period Average (LPA)

The average rainfall recorded over a specific period (usually 50 years) used as a benchmark for monsoon performance.

Current Fact: The IMD predicted an above-normal monsoon for 2025 at 105% of the LPA on April 16, 2025.

Somali Jet

A low-level cross-equatorial jet stream that intensifies during the summer to transport moisture from the Indian Ocean to the subcontinent.

Current Fact: Strengthening of the Somali Jet was a key factor in the early 2025 monsoon arrival mentioned in May 2025 reports.

Mascarene High

A high-pressure area in the southern Indian Ocean whose intensity determines the strength of the southwest monsoon winds.

Current Fact: Intensification of the Mascarene High was reported on May 28, 2025, as a driver for the early monsoon surge.

What Happens Next

Current Status

As of February 2, 2026, the IMD has indicated a 2026 return of the El Niño phenomenon after July, with full clarity expected by April 2026.

Likely Next

A probable 'April Forecast' by the IMD which will determine the initial rainfall outlook for the 2026 southwest monsoon.

Wildcards

The development of a positive Indian Ocean Dipole (IOD) could potentially offset a weak El Niño, whereas a 'Super El Niño' could trigger severe drought.

Why UPSC Cares

Syllabus Topics

• Important Geophysical phenomena (Earthquakes, Tsunami, Volcanic activity, Cyclone etc.)
• Changes in critical geographical features and their effect on flora and fauna
• Direct and indirect farm subsidies and minimum support prices; Public Distribution System

Essay Angles

• The Economic Cost of Climate Volatility in Agrarian Societies
• Science vs. Uncertainty: The Evolution of Monsoon Forecasting in India

Prelims Likely: Yes

Mains Likely: Yes

Trend Signal: perennial

Exam Intelligence

Previous Year Question Connections

• Differences between La Niña and El Niño and their impacts. — The arc provides a real-time example of the transition between these phases (Neutral to La Niña to El Niño) and their specific impacts on the Indian context.
• Indian Ocean Dipole (IOD) and El Niño interaction. — Matches the 'Neutral ENSO' context where secondary factors like IOD or MJO (mentioned in May 2025) become the dominant drivers of rainfall.

Prelims Angles

• The specific percentage of LPA (105%) that defines an 'Above Normal' monsoon.
• The direction of the Somali Jet (South-westerly) and its seasonal intensification period (June-August).
• The location of the Mascarene High (South Indian Ocean near Madagascar) and its role in the Indian monsoon.
• The normal onset dates for the South Andaman Sea (mid-May) vs Kerala (June 1).

Mains Preparation

Sample Question: Examine the role of non-ENSO factors, such as the Madden-Julian Oscillation (MJO) and the Somali Jet, in influencing the timing and intensity of the Indian monsoon. Discuss in the context of the 2025-26 weather cycle.

Answer Structure: Intro: Define ENSO phases and the 2025 context → Body 1: Explain the MJO's mechanism and how it triggered the early 2025 onset → Body 2: Role of Somali Jet and Mascarene High in moisture transport → Critical Analysis: Why ENSO neutral years increase reliance on these local/transient factors → Way Forward: Need for better sub-seasonal to seasonal (S2S) forecasting.

Essay Topic: Unpredictable Monsoons: The Achilles' Heel of Indian Economic Planning.

Textbook Connections

Key Takeaway

The 2025-26 cycle demonstrates that while ENSO is the primary long-range indicator, short-term phenomena like the MJO can radically alter monsoon onset and intensity, necessitating high-resolution meteorological monitoring.

All Events in This Story (9 items)

1. 2025-04-01 [Geography] — IMD Predicts Warmer Summer
   The India Meteorological Department (IMD) has ruled out the possibility of an El Nino during the coming southwest monsoon season this year but predicted a warmer summer.
   More details

   UPSC Angle: IMD predicts warmer summer, rules out El Nino for southwest monsoon.

   Key Facts:

   • Organization: India Meteorological Department (IMD)
   • Prediction: Warmer summer
   • Monsoon: El Nino unlikely
2. 2025-04-12 [Geography] — El Niño-Southern Oscillation (ENSO) Forecast
   The National Oceanic and Atmospheric Administration (NOAA) has forecasted that neutral conditions will dominate the Pacific Ocean until October 2025. ENSO is a climate phenomenon resulting from interactions between the ocean and atmosphere in the equatorial Pacific Ocean. It has three phases: El Niño, La Niña and Neutral.
   More details

   UPSC Angle: NOAA forecasts neutral ENSO conditions until October 2025.

   Key Facts:

   • Neutral conditions in the Pacific Ocean are expected until October 2025.
3. 2025-04-16 [Geography] — IMD Predicts Above-Normal Monsoon
   The Indian Meteorological Department (IMD) has predicted an above-normal monsoon, forecasting 105% of the normal rainfall. Conditions are favorable for rainfall to be above normal. The long period average for the upcoming June-September monsoon season is expected to be above normal.
   More details

   UPSC Angle: IMD predicts above-normal monsoon, forecasting 105% of normal rainfall.

   Key Facts:

   • IMD predicts: Above-normal monsoon.
   • Rainfall forecast: 105% of normal.
   • Season: June-September.
4. 2025-05-08 [Geography] — Early Onset of Southwest Monsoon
   The India Meteorological Department (IMD) indicated chances of an early onset of the southwest monsoon. The normal date for the onset of monsoon over the South Andaman Sea is anytime after mid May, with the normal date being May 19. The monsoon advances close to mainland India by late May, and IMD declares the monsoon onset over India when it hits Kerala, where the normal onset date is June 1.
   More details

   UPSC Angle: Not exam-relevant

   Key Facts:

   • Normal date for monsoon onset over the South Andaman Sea: anytime after mid-May, normally May 19.
   • Normal date for monsoon onset over Kerala: June 1.
5. 2025-05-28 [Geography] — Early Monsoon Onset Triggered by Madden-Julian Oscillation (MJO)
   The early onset of the southwest monsoon in Kerala and Mumbai was triggered by the Madden-Julian Oscillation (MJO), a moving system of winds, clouds, and pressure that enhances rainfall. The MJO, along with other factors like the intensification of the Mascarene High, a convection surge, and strengthening of the Somali Jet, contributed to the early arrival of monsoon currents. Mumbai experienced its wettest May in over 100 years.
   More details

   UPSC Angle: Early monsoon onset triggered by Madden-Julian Oscillation (MJO).

   Key Facts:

   • Mascarene High intensification.
   • Convection surge.
   • Somali Jet strengthening.
   • Heat low formation.
   • Early monsoon onset in Kerala and Mumbai triggered by Madden-Julian Oscillation (MJO).
   • MJO is a moving system of winds, clouds, and pressure.
   • MJO circles the globe typically every 30–60 days.
   • Other contributing factors: Mascarene High intensification, convection surge, and Somali Jet strengthening.
6. 2025-07-01 [Geography] — India to get above-normal rain in July, forecasts IMD
   The India Meteorological Department (IMD) has predicted that India will experience above-normal rainfall in July. This forecast is crucial for agriculture and water resource management across the country.
   More details

   UPSC Angle: IMD forecasts above-normal rainfall in India for July.

   Key Facts:

   • India
   • above-normal rain
   • July
   • IMD
7. 2025-09-02 [Environment & Ecology] — UN Warns La Niña Return Won't Stop Global Temperature Rise
   UN weather experts indicate that the cooling climate phenomenon, La Niña, could already be back, but they warn it won't stop the trend for warmer global temperatures caused by human activity. The World Meteorological Organization (WMO) indicates a 55% likelihood that sea temperatures in the equatorial Pacific will cool as of this month.
   More details

   UPSC Angle: La Niña won't stop global temperature rise, says UN.

   Key Facts:

   • La Niña could be back
   • 55% likelihood of cooling sea temperatures in the equatorial Pacific
8. 2025-11-03 [Geography] — India Meteorological Department forecasts mixed weather
   The India Meteorological Department (IMD) forecasts a mixed weather week for India as November begins. A fresh western disturbance is expected to bring light rain and snowfall to the northern hills starting November 3, signaling pre-winter conditions, while thunderstorms are expected to continue over western and coastal regions. The IMD has clarified that northwest India is unlikely to experience an unusually harsh winter this month, with weather conditions expected to remain largely normal, similar to previous years.
   More details

   UPSC Angle: Not exam-relevant

   Key Facts:

   • A fresh western disturbance is set to influence northwest India from the night of November 3, 2025.
   • Light to moderate rainfall and snowfall is expected over the western Himalayan region between November 3 and 5, 2025.
   • States like Himachal Pradesh and Uttarakhand will be affected.
   • Thunderstorms are likely over the Andaman Islands and western Madhya Pradesh by November 3, 2025.
   • La Nia conditions are likely to persist from November to December 2025.
   • Negative IOD conditions are expected to weaken in the coming months.
9. 2026-02-02 [Geography] — El Nino Phenomenon
   There is a chance that the El Nino phenomenon may occur after July this year, but clarity will only emerge in April, according to the director-general of the India Meteorological Department (IMD). In India, El Niño causes weak rainfall and more heat.
   More details

   UPSC Angle: El Nino phenomenon may occur after July this year.

   Key Facts:

   • El Nino phenomenon may occur after July 2026
   • Clarity will emerge in April
   • In India, El Niño causes weak rainfall and more heat