India’s monsoon extremes explained: ‘Blockade’ over Iran played a dangerous role

(Image: PTI)

Northwest India’s recent spell of intense rainfall, which led to widespread disruption, was the result of a rare and powerful convergence of multiple weather systems. While the monsoon is the primary source of summer rain, the exceptional severity of these downpours was due to an unusual player entering the stage at an unexpected time: a series of western disturbances.

The meteorological patterns behind the event explains the complex interaction between these systems as the primary cause for the extreme weather.

What are the reasons behind extreme weather in India?

The foundational element of the heavy rain was the monsoon trough, a constant feature of the season. This elongated low-pressure zone channels moist air inland from the Bay of Bengal. Within this trough, cyclonic circulations create an anti-clockwise movement of air, pulling in more moisture and forcing it upward. As the air rises, it cools and condenses, forming rain clouds.

Four such systems developed in quick succession during the second half of August alone. However, the presence of this trough does not automatically guarantee severe rainfall everywhere along its path, which is what made the recent event in northwestern states so notable.

Why northwest India is hit by extreme rainfall?


The critical intensifying factor was the presence of western disturbances. These storm systems, which originate over the Mediterranean Sea, typically affect northern India but are usually absent during the peak monsoon months of July and August.

Their frequency this August was highly abnormal. According to a long-term data set created by Kieran Hunt, a climate researcher at the University of Reading, cited in the HT report, the historical average for August between 1971-2020 is just 1.42 western disturbances, with some years recording none. In a significant anomaly, five such storms affected India in August 2025.

Very unsual: Why did western disturbances appear in peak monsoon?

A full explanation requires further study, but meteorologists point to a phenomenon known as atmospheric blocking. Between August 25-27, high-level wind patterns became stagnant north of Iran, creating a blocking pattern. This acted like a atmospheric roadblock, disrupting the normal path of western disturbances and shunting them southward towards northern India instead.

This set the stage for a dangerous interaction. Research scientist Akshay Deoras was cited by HT as explaining that whilst the monsoon supplies the moisture required for heavy rainfall, a western disturbance can act as a catalyst, translating that available moisture into widespread and heavy precipitation. He noted that such interactions are far more common before the monsoon's onset or after its withdrawal compared to August.

How atmospheric convergence fuelled extreme monsoon rain?

The convergence of these systems supercharges rainfall through specific mechanisms. According to scientific literature, including a 2021 paper by Hunt, a western disturbance can either physically merge with a monsoon low or, as was the case in this late-August event, enhance the overall atmospheric conditions for heavy rain production without a full merger.

This enhancement creates a more efficient and violent process of converting the monsoon's abundant moisture into precipitation, leading to the severe downpours that battered regions like Jammu and Kashmir. The event exemplifies how the unexpected interplay between global and regional weather patterns can lead to extreme localised weather.