Impact transition of spring North Pacific Oscillation on the Northwest Pacific tropical cyclone during autumn

The North Pacific Oscillation (NPO) is the second dominant mode in the Northern Pacific sea-level pressure, exerting significant influences on the tropical cyclone (TC) over the western North Pacific (WNP). While studies show that the spatial pattern of NPO has undergone interdecadal changes, the impact of these changes on the NPO-TC relationship is unclear. Here we reveal that this relationship experienced an interdecadal shift from positive to negative correlation around 2004/2005. During the earlier period (1986–2004), the NPO induced a persistent cold pool over the WNP, which promoted northerly winds, enhancing subsidence and reduced relative humidity to suppress TC genesis. In contrast, during the later period (2005–2023), the southern lobe of the NPO extended northwestward, which led to the development of a localized warm pool over the subtropical WNP. The expanding warm pool persisted into autumn and contributed to a cyclonic circulation centered over the Philippines Sea, which enhanced upward motion and moisture convergence to promote TC genesis. Our findings provide important insights into the mechanisms driving interdecadal variability in TC activity and highlight the role of springtime NPO in improving seasonal prediction models under ongoing climate change.