Increasing Frequency of Extremely Severe Cyclonic Storms in the North Indian Ocean by Anthropogenic Warming and Southwest Monsoon Weakening

North Indian Ocean (NIO) has shown an increase in the frequency of extremely severe and higher‐category cyclonic storms (ESCS), with maximum frequency during May. Analyses of data sets and coupled model experiments reveal that anomalous increase in Potential intensity (PI) and ocean heat‐content with higher increase during May and weakening summer monsoon circulation has led to increasing ESCS with peak frequency during May. PI is a function of environmental conditions that influence thermodynamic atmosphere–ocean disequilibrium and thermodynamic efficiency. Increase in air‐sea disequilibrium by the accelerated warming of NIO dominates the PI trend, contributes more than 70% of PI trend, remaining by the thermodynamic efficiency from increased tropical‐tropopause layer cooling. Additionally, weakening of summer monsoon circulation weakens vertical wind‐shear, weakens southward ocean heat‐transport and enhances heat accumulation, leading to increase in ESCS. Projected changes in PI and wind‐shear may further increase ESCS, making densely populated NIO region vulnerable to climate change. Plain Language Summary This study identifies a mechanism for the increasing frequency of extremely severe and higher category cyclonic storms in the north Indian Ocean (NIO), with maximum frequency during May. NIO region is dominated by the summer monsoon circulation and as a result the sea surface temperature and potential intensity have a semi‐annual cycle with peak during May. Accelerated warming of the NIO dominates the potential intensity trend with highest increase during May. Tropical tropopause layer cooling also contributes to the increase in potential intensity. Additionally, weakening of summer monsoon circulation weakens the vertical wind shear during May–October. In addition, weakening monsoon increases the heat accumulation in the NIO by weakening southward ocean heat transport. These in‐turn lead to increasing extremely severe and higher‐category cyclonic storms, with higher frequency during May. Projected increase in the potential intensity and weakening of vertical wind shear over the 21st century caution possible increase in higher‐category cyclonic storms in NIO, demanding policies and planning for defending coastal flood risk and associated impacts. Key Points North Indian Ocean has shown an increase in the frequency of extremely severe and higher‐category cyclonic storms, especially during May Increase in Potential intensity with higher increase during