Change in Tropical Cyclone Efficiency Under Different ENSO Conditions in the Western North Pacific Ocean

Abstract Tropical cyclones (TCs) can be considered as Carnot heat engines, where thermodynamic efficiency depends on the sea surface temperature (SST) and TC outflow temperature ( T o ) in the upper atmosphere. This study investigates how TC efficiency in the western North Pacific (WNP) Ocean varies under different El Niño‐Southern Oscillation (ENSO) conditions: the Eastern Pacific (EP), the Central Pacific (CP), and the Mixed El Niño types, as well as La Niña. We also explore how these changes affect a TC's theoretical upper bound (potential intensity (PI)). Using a reanalysis data set from 1979 to 2024, we find that TC efficiency decreases during La Niña, due to warmer T o , and increases during CP El Niño, where upper‐level cooling dominates. EP and Mixed El Niño show more heterogeneous responses. These efficiency changes contribute to PI variability from −38 to +27%, depending on ENSO type and region.