Modulation of Tropical Waves on Developing and Non‐developing Tropical Disturbances Over the Western North Pacific

Tropical waves, including Madden−Julian Oscillation (MJO), equatorial Rossby (ER) waves, and Kelvin waves, potentially play crucial roles in the genesis of tropical cyclones (TCs). However, their influence during the precursory stage of TC genesis remains poorly understood. This study compares the impact of these tropical waves on disturbances that ultimately develop into TCs (i.e., developing disturbances) versus those that do not (i.e., non‐developing disturbances). Using reanalysis, satellite precipitation, and TC best‐track data sets from 2000 to 2019, we identify developing and non‐developing disturbances and their associated tropical waves during 3‐day period over the western North Pacific. Composite analyses under the Lagrangian framework reveal that all tropical waves are related to both types of disturbances, with MJO and ER waves showing the most significant differences between two types of disturbances during a 3‐day period. Developing disturbances are more frequently linked to the active MJO phases and higher MJO amplitudes, while non‐developing disturbances are more often associated with inactive MJO phases. MJO‐induced westerly anomalies and enhanced precipitation in developing disturbances promote cyclonic vorticity and barotropic energy conversion, enhancing upper‐level divergence and mid‐level moisture, fostering intensification of tropical disturbances. ER waves similarly contribute to stronger precipitation and cyclonic vorticity near the center of developing disturbances, inducing stronger eddy kinetic energy in the middle and lower troposphere, supporting intensification of tropical disturbances. Kelvin waves contribute to developing disturbances by enhancing upper‐level divergence and low‐level vorticity one or 2 days before TC genesis.