While the effects of the recent heavy rainfall across northwest India have been a painful reality for many, the meteorological science behind these deluges reveals a complex and unusual interaction of multiple weather phenomena. Experts point to a rare “dangerous harmony” between low-pressure systems, cyclonic circulations, and an unseasonal abundance of Western Disturbances as the cause of the extreme weather.
Low-Pressure Systems and Cyclonic Circulations
At the heart of the monsoon system are low-pressure systems and cyclonic circulations. Low-pressure zones act like atmospheric vacuums, drawing in air from surrounding high-pressure areas. As this air rushes inward, it also moves upward, cools, and condenses its moisture, leading to rainfall. In the Northern Hemisphere, this inward-spiraling movement of air forms a counter-clockwise flow known as a cyclonic circulation.
During the monsoon season, these low-pressure regions often form an elongated shape called the monsoon trough, which typically runs from the Bay of Bengal into the northwestern states. This trough acts as a conveyor belt for moisture, and when it is particularly active, it can lead to widespread rainfall. According to the report, four such systems have affected India in the second half of August alone.
Western Disturbances: The Unexpected Catalyst
While the monsoon trough is a regular feature of India’s summer, the recent intensity of rain in the northwest has been largely attributed to an unusual number of Western Disturbances. These are extratropical storms that originate in the Mediterranean region and typically bring winter rains and snowfall to northern India. They are not usually a factor during the peak monsoon months of July and August.
However, in a highly unusual turn of events, five such storms affected India in August 2025. This is far above the long-term average of just 1.42 Western Disturbances for the month, based on data from 1971-2020. According to Akshay Deoras, a research scientist at the University of Reading, a Western Disturbance “can act like a catalyst, translating available moisture into widespread and heavy precipitation.” This interaction is a key factor behind the recent extreme weather.
The Mechanism of Interaction
The intense deluges are the result of these two distinct weather systems—the tropical monsoon and the extratropical Western Disturbances—working in concert. As noted in a 2021 paper by climate researcher Kieran Hunt, Western Disturbances intensify monsoon rain through two main mechanisms.
In the case of the devastating 2013 Uttarakhand floods, a Western Disturbance directly supplied moisture to a monsoon system. However, the August 2025 event exemplified a different type of interaction, where the Western Disturbances enhanced the overall conditions for heavy rain rather than directly merging with the monsoon system. A likely contributing factor was atmospheric blocking over Iran, which caused high-altitude wind patterns to become stagnant and diverted the Western Disturbances southward toward northern India.
This rare meteorological alignment of a strong monsoon trough and an unseasonal influx of Western Disturbances has created a perfect storm, leading to the unprecedented heavy rainfall and the resulting floods and landslides in Jammu and Kashmir, Himachal Pradesh, and other parts of northwest India. The India Meteorological Department has since warned that above-normal rainfall is expected to continue in September, which could exacerbate the flood and landslide situation in the region.