Bhubaneswar: Cyclones hitting India’s eastern coast are weakening slowly after landfall, especially during the post-monsoon season, a new study by IIT Bhubaneswar and the India Meteorological Department (IMD) has revealed. Researchers also found that post-monsoon cyclones now take about 50% longer to lose strength compared to those in the pre-monsoon phase.By studying cyclone data from 1995 to 2024, scientists have found that in the last two decades, post-monsoon cyclones are now taking about 34 hours to weaken significantly after landfall. In contrast, pre-monsoon cyclones (from March to May) weaken much faster — in about 22 hours.Given that most of the cyclones (73%) in the Bay of Bengal are post-monsoon, overall cyclones today are surviving longer over land, increasing the risk of strong winds and heavy rain for inland areas and in turn, causing more damage. The study pointed out that if cyclones stay strong longer, damage can spread much farther inland.Traditionally, cyclones weaken quickly once they hit land because they lose their main energy source — warm ocean water. However, researchers found that this is no longer happening as fast as before, especially during the post-monsoon phase (Oct to Dec).The key reason lies within the cyclone itself — in a region called the eyewall, which surrounds the calm centre or ‘eye’ of the storm. The eyewall contains intense clouds, strong wind and heavy rainfall. If this structure remains well organised and balanced, the cyclone can continue even after it crosses the coast.The study found that cyclones with a strong, circular (symmetric) eyewall weaken slowly, and those with disturbed or uneven eyewalls weaken quickly. Some recent cyclones managed to protect their eyewall structure, allowing them to last longer after landfall.“Out of 83 tropical cyclones that formed in the Bay of Bengal from 1995 to 2024, as many as 66 had made landfall, and 73% of those were in the post-monsoon season. Mostly, pre-monsoon cyclones made landfall over northern Odisha, West Bengal, and Myanmar coast. However, the landfall locations for post-monsoon cyclones vary widely over the eastern coast of India and Bangladesh,” the study pointed out.Cyclones such as Titli (2018) and Gaja (2018) showed this behaviour, which allowed them to maintain strength for several hours after landfall, revealed the research which was recently published in the Quarterly Journal of the Royal Meteorological Society.On the other hand, cyclones Hudhud (2014) and Vardah (2016) weakened rapidly because their eyewall structure broke down quickly, dry air from land entered the cyclone, and their internal balance was disturbed after landfall.With climate change increasing the risks of extreme weather events, understanding why cyclones lose strength slowly can be crucial to disaster planning, early warning systems, and saving lives and reducing losses, said the researchers.The study was conducted by Sandeep Pattnaik and Sankhasubhra Chakraborty, researchers from IIT Bhubaneswar, and BAM Kannan of the IMD, Chennai.
