Madden-Julian Oscillation Helped the Monsoon Arrive Early

As stated by the India Meteorological Department (IMD), the Madden-Julian Oscillation (MJO) was crucial in this occurrence.

What does Madden-Julian Oscillation (MJO) refer to?

The MJO is a dynamic system of winds, clouds, and pressure that delivers rainfall as it rotates around the equator.

It was found in 1971 by Roland Madden and Paul Julian.

The system moves east at speeds of 4–8 m/s and usually completes a full circuit around the Earth in 30–60 days, although it may require as much as 90 days.

As it progresses, intense MJO activity frequently divides the globe into two sections — one where the MJO is in its active phase, causing rain, and the other where it inhibits rainfall.

Geographical Impact

The influence of the MJO is primarily observed in the tropical zone, within the area stretching from 30 degrees North to 30 degrees South of the equator, although its effects are also experienced in the mid-latitude areas of both hemispheres.

It also encompasses India, positioning it as a key participant in the South Asian monsoon system.

In an active MJO phase, areas affected by it see higher-than-normal rainfall, frequently attributed to enhanced cloud development, convection, and cyclonic processes.

Impact of MJO on the Early Monsoon

This year, the MJO was detected in Phase 4 with an amplitude exceeding 1 on about May 22, starting in the Indian Ocean.

Phase 4 with high amplitude signifies heavy rainfall and storm systems, favorable for the start of the monsoon.

This arrangement led to regular cyclonic events and cloud formation over the Bay of Bengal, facilitating the early onset of the monsoon in Kerala.

Additional causes for Early Monsoon

Transition to La Niña: In early 2025, international climate models suggested a weakening of El Niño and the potential onset of La Niña — a trend historically linked to more intense and earlier monsoon periods in India.

More powerful cross-equatorial winds than normal: In May, southern hemisphere winds start to sweep across the equator and reach the Arabian Sea.

When these winds are more powerful and structured, they drive moist air toward the Indian coast faster, speeding up the onset of the monsoon.

Elevated sea surface temperatures: Hotter-than-normal waters in the Arabian Sea and Bay of Bengal stimulate strong convection, facilitating the formation of cloud bands and low-pressure systems essential for monsoon development.

In 2025, the region's sea surface temperatures exceeded the average, facilitating early cloud formation.

Final thoughts

Although the early arrival of the monsoon provides essential benefits for agriculture and water resource management, it also heightens vulnerabilities linked to climate change.

With monsoon patterns growing more unpredictable due to climate change, enhancing early warning systems and forecasting models is crucial for protecting lives, livelihoods, and ecosystems.