Distinct Characteristics of Tropical Cyclone Activity over the Western North Pacific during Multi-year La Niña Events

Abstract The increasing frequency of multi-year La Niña events in recent decades has led to worldwide weather-related hazards, yet the evolution of tropical cyclone (TC) activity over the western North Pacific (WNP) during the developing year of these events remains unclear. Here, we show that multi-year La Niña events generally suppress WNP TC activity, resulting in a significant reductions in both TC genesis and track frequency. Notably, TC activity exhibits distinct features in the first year and successive year of multi-year La Niña events. For the first year, TC activity is significantly suppressed with only 20.7 TCs formed over the WNP due to the unfavorable large-scale conditions associated with the anti-cyclonic circulation over the WNP from January to August, which is maintained by the Indo-Pacific capacitor feedback following the preceding El Niño. In contrast, during the successive year, TC genesis frequency in the Philippine Sea increases throughout the year due to the anomalous convergence associated with the residual SST cooling in the equatorial Pacific and the La Niña initiated SST cooling in the equatorial Indian Ocean. This increased TC genesis offests the decrease in the eastern WNP, leading to a total TC number close to the climatology of 25.9. Nevertheless, due to the westward shift in TC genesis location, TC track frequency significantly decreases in both the first year and successive year. These findings highlight the substantial but distinct influences of multi-year La Niña events on WNP TC activity in their first year and successive year and offer valuable insights for improving seasonal and multi-year TC predictions in this region.