Delhi rains: What is causing unseasonal storms, heavy rainfall in Delhi-NCR? IMD says reason is...

India.com

25-05-2025

Delhi was lashed by unseasonal heavy rains and thunderstorms on Saturday. (ANI/File)
Delhi rains: Delhi and its surrounding National Capital Region (NCR) was hit by pre-monsoon heavy rains, accompanied by gusty winds and thunderstorms that brought relief to people from the sweltering summer heat. However, such type of weather is not usually expected in the months of April to mid-May before the onset of monsoon.
Then, what is causing these unseasonal storms and heavy rains in the Delhi-NCR region? The answer lies in the now undeniable climate change, which has caused the Kalabaisakhi or Nor'wester– a pre-monsoon phenomenon which is commonly associated with Eastern India, but has now presumably expanded to the Northern region due to changing climate patterns, according to weather agencies. What is a Nor'wester aka Kalabaisakhi?
Locally known as Kalbaisakhi, a Nor'wester is a pre-monsoon phenomenon that usually occurs in Eastern parts of the country, bringing sudden heavy rains, accompanied by strong winds and severe thunderstorms in states like West Bengal, Odisha, Assam, Jharkhand, and Bihar, and some of parts of neighboring Bangladesh.
The 'Nor'wester' is so named because storm usually moves from the northwest towards the east, while its local name 'Kalbaisakhi' loosely translates to 'calamity that strikes in the month of Baisakh (April-May).
A Nor'wester or Kalbaisakhi storm is characterized by strong, powerful winds that can exceed 100 km/h, and move in a straight line akin to a Derecho– a wind pattern where winds move in a straight line unlike a Tornado, which is distinguished by its curly wind pattern. The pre-monsoon storm is often accompanied by sudden, heavy rainfall, which can trigger flash floods, akin to what was witnessed in Delhi-NCR on late Saturday night. What caused heavy rains, pre-monsoon storms in Delhi NCR?
According to weather agencies, various weather phenomenon are responsible for Saturday's intense spell of heavy rains and thunderstorms in Delhi-NCR region such as western disturbances, which are low-pressure systems originating from the Mediterranean region that trigger unseasonal showers in north India, including the national capital.
Additionally, upper cyclonic circulations over nearby over nearby regions like Haryana or Rajasthan, can lead to heavy rains and thunderstorms in Delhi-NCR. A recent spell of rains in Delhi-NCR is being attributed to this weather system.
Apart from the above factors, other phenomenon such as convective systems, which are created by rapid upward movement of humid, moist air, can cause thunderstorms in Northern India. Further, the influence of monsoon trough starts increasing by late May when it moves south from its normal normal position, increasing moisture and contributing to stormy weather in the region.