Post-Monsoon Cyclones Weakening Slower, Posing Greater Inland Threats: IIT Bhubaneswar-IMD Study
A groundbreaking collaborative study conducted by researchers from the Indian Institute of Technology (IIT) Bhubaneswar and the India Meteorological Department (IMD) has uncovered a critical shift in the behavior of cyclones impacting India's eastern coastline. The research reveals that cyclones striking during the post-monsoon season are now weakening at a significantly slower rate after making landfall compared to their pre-monsoon counterparts.
Alarming Slowdown in Weakening Patterns
By meticulously analyzing comprehensive cyclone data spanning from 1995 to 2024, scientists have identified a troubling trend. Post-monsoon cyclones, which occur from October to December, now require approximately 34 hours to weaken substantially after crossing the coast. In stark contrast, pre-monsoon cyclones (March to May) dissipate much more rapidly, typically losing strength within about 22 hours. This represents a dramatic 50% longer duration for post-monsoon cyclones to lose their intensity.
This extended lifespan over land carries profound implications for disaster management and public safety. Since the majority of Bay of Bengal cyclones—approximately 73%—occur during the post-monsoon season, the overall trend indicates that cyclones today are persisting longer over terrestrial areas. This prolonged activity significantly elevates the risk of destructive strong winds and torrential rainfall penetrating far inland, potentially causing more extensive damage to infrastructure, agriculture, and communities.
The Crucial Role of the Eyewall Structure
Traditionally, cyclones rapidly lose power upon landfall as they are deprived of their primary energy source: warm ocean waters. However, this study demonstrates that this weakening process is no longer occurring as swiftly as historically observed, particularly in the post-monsoon phase. The key to this resilience lies within the cyclone's internal architecture, specifically the eyewall region.
The eyewall, which encircles the calm central eye of the storm, is characterized by intense cloud formations, ferocious winds, and heavy precipitation. Researchers found that when this structure remains well-organized, symmetrical, and balanced, the cyclone can maintain its coherence and strength even after moving over land. Conversely, cyclones with disturbed, uneven, or fragmented eyewalls tend to disintegrate quickly following landfall.
Notable examples include cyclones Titli (2018) and Gaja (2018), which successfully preserved their eyewall integrity, allowing them to retain destructive potential for several hours after crossing the coastline. In contrast, cyclones like Hudhud (2014) and Vardah (2016) weakened rapidly because their eyewall structures collapsed promptly, enabling dry continental air to infiltrate the system and disrupt its internal thermodynamic balance.
Detailed Findings and Geographic Patterns
The study examined 83 tropical cyclones that developed in the Bay of Bengal between 1995 and 2024. Of these, 66 made landfall, with the overwhelming majority—73%—occurring during the post-monsoon season. The research also highlighted distinct geographic patterns in landfall locations.
Pre-monsoon cyclones predominantly strike the northern Odisha coast, West Bengal, and the Myanmar coastline. Post-monsoon cyclones, however, demonstrate much wider variability, affecting extensive stretches of the eastern Indian seaboard and Bangladesh. This dispersion further complicates preparedness and response efforts for vulnerable regions.
Implications for Climate Change and Disaster Preparedness
As climate change continues to amplify the frequency and intensity of extreme weather events globally, understanding these evolving cyclone dynamics becomes increasingly vital. The researchers emphasize that insights into why cyclones are losing strength more slowly are crucial for enhancing disaster planning, refining early warning systems, and ultimately saving lives and minimizing economic losses.
The study, recently published in the prestigious Quarterly Journal of the Royal Meteorological Society, was authored by Sandeep Pattnaik and Sankhasubhra Chakraborty from IIT Bhubaneswar, in collaboration with BAM Kannan from the IMD office in Chennai. Their work underscores the urgent need for updated meteorological models and adaptive risk management strategies to address this emerging threat to coastal and inland communities across eastern India.
