Tropical Cyclone Activity and ENSO Influence in the Western North Pacific

The western North Pacific basin exhibits the highest frequency of tropical cyclones globally, with marked interannual and interdecadal variability driven largely by the El Niño–Southern Oscillation (ENSO). In El Niño years, anomalous warming in the central and eastern Pacific shifts the genesis region eastward, alters low-level vorticity and enhances vertical wind shear near the Philippines, often reducing storm counts in the South China Sea. Conversely, La Niña phases favour higher cyclone frequency closer to the Asian coast. Superimposed on these ENSO effects are longer-term modulations by the Pacific Decadal Oscillation and other climate modes, which together influence seasonal risk patterns, track density and landfall probabilities critical for disaster preparedness across East and Southeast Asia.

Research from Nature Portfolio

Recent analyses of the 2018 typhoon season revealed two contrasting extremes: an exceptionally active summer marked by a pronounced northward shift of genesis points, followed by one of the weakest autumnal seasons on record. These anomalies were attributed primarily to a strong El Niño Modoki event reinforcing a Pacific Meridional Mode positive phase, which together intensified low-level cyclonic circulation in boreal summer. In autumn, a developing anticyclonic anomaly over the South China Sea—linked to an active Indian Ocean Dipole—suppressed convection and halted cyclone formation. Numerical experiments underscored the interplay of these basin-scale drivers in modulating both the spatial distribution and overall activity of tropical cyclones.

Tropical Cyclone Activity and ENSO Influence in the Western North Pacific publication trend

The graph below shows the total number of articles in tropical cyclone activity and enso influence in the western north pacific across all publications each year (not limited to Nature Index journals).

Technical terms

El Niño–Southern Oscillation (ENSO): A coupled ocean–atmosphere phenomenon in the tropical Pacific that alternates between warm (El Niño) and cool (La Niña) phases, modulating global weather patterns and tropical cyclone activity.

Tropical cyclone genesis frequency (TCGF): The number of cyclones formed within a specified region and time period, used as a metric for interannual and decadal variability.

Pacific Meridional Mode (PMM): A climate variability pattern characterised by SST and wind anomalies in the northeast Pacific that can precondition ENSO events and influence regional cyclone environments.

Vertical wind shear: The difference in wind speed or direction between two atmospheric levels; strong shear often inhibits cyclone intensification by displacing convection.

References

1. On the relationship between ENSO and tropical cyclones in the western North Pacific during the boreal summer. Climate Dynamics (2018).
2. Western North Pacific Tropical Cyclone Activity in 2018: A Season of Extremes. Scientific Reports (2020).
3. Atmospheric modes fiddling the simulated ENSO impact on tropical cyclone genesis over the Northwest Pacific. npj Climate and Atmospheric Science (2023).
4. Shifted relationship between the Pacific decadal oscillation and western North Pacific tropical cyclogenesis since the 1990s. Environmental Research Letters (2024).
5. Skillful Seasonal Prediction of Typhoon Track Density Using Deep Learning. Remote Sensing (2023).