Tropical Cyclone Trends in the Western North Pacific and Relation with ENSO

Understanding changes in tropical cyclone (TC) behavior in the Western North Pacific (WNP) is essential for improving prediction and disaster prevention. Using Japan Meteorological Agency’s best-track data and NOAA El Niño/Southern Oscillation (ENSO) indices (1979–2023), this study examined long-term trends in TC frequency, intensity, radius, translation speed, and position migration, along with their relationship with El Niño–Southern Oscillation (ENSO). Results showed that the annual TC frequency displayed no significant trend, but the 10-year running mean revealed a substantial decline. Furthermore, although the TC intensity displayed no robust monotonic trend, the structural shift around 2001 suggested changing environmental controls. ENSO strongly modulated TC intensity, with El Niño years producing a considerably higher mean intensity and lifetime maximum intensity (LMI) than La Niña years. LMI locations occurred equatorward and eastward during El Niño, and northwestward during La Niña, with long-term poleward (0.016°N/yr) and westward (−0.067°E/yr) migration. The radius of the maximum wind (R_max) showed no secular trend but contracted during El Niño and expanded during La Niña. The translation speed at LMI increased by about 14%, mainly due to poleward shifts into relatively strong steering flows, with little ENSO influence. These results highlighted the combined effects of climate change and ENSO on TC behavior in the WNP.