New Delhi: Delhi-NCR has been reeling under intense thunderstorms, gusty winds, and heavy rainfall over the past few days, an unusual occurrence for mid-May. While the showers have brought a much-needed break from the oppressive summer heat, the timing and intensity have left meteorologists and residents equally surprised. This unusual weather may be the result of shifting climatic patterns and multiple active systems, including a phenomenon more typical of eastern India known as Kalbaisakhi.
What Is Kalbaisakhi?
Kalbaisakhi, or Nor’wester, is a type of severe thunderstorm that usually strikes the eastern parts of India, mainly West Bengal, Odisha, Assam, Bihar and Jharkhand, during the pre-monsoon season in April and May.
The term “Kalbaisakhi” means “calamity of the Baisakh month” in Bengali, while the English name "Nor’wester" refers to the storm’s direction of movement: from the northwest to the east. These storms are short-lived but violent, often marked by sudden strong winds, lightning, and torrential rain.
Characteristics of Kalbaisakhi storms include:
Strong straight-line winds, sometimes exceeding 100 km/h, resembling a weather phenomenon known as derecho.
Intense downpours that can lead to flash flooding, similar to what was observed in Delhi-NCR around 2 am on Sunday.
Occasional hailstorms or even tornado-like winds, depending on atmospheric instability.
Bow echo patterns on weather radar, signifying an organised and forceful convective system.
Though Kalbaisakhi is typically an eastern India event, the presence of similar atmospheric conditions in Delhi-NCR suggests that a Nor’wester-like system may have shifted westward, a sign of changing climate dynamics.
Several weather systems collectively triggered this unusual episode in Delhi-NCR. A Western Disturbance, a Mediterranean-origin low-pressure system, collided with moist air from both the Arabian Sea and the Bay of Bengal, leading to widespread thunderstorms. Simultaneously, an upper air cyclonic circulation over Haryana and Punjab provided the right trigger for convective activity.
Added to this was a convective system, formed by intense surface heating and increased humidity, which caused vertical air movement and led to thunderstorms. Lastly, the monsoon trough, which typically shifts northward in June, has already started influencing northern India. Its southward dip helped enhance moisture and played a supporting role in this weather episode.
