Reproducing the Extreme 1959 Tropical Cyclone Season over the Western North Pacific Using a High-Resolution Model

Accurately reproducing historical extreme tropical cyclone (TC) seasons is essential for understanding the physical mechanisms governing TC intensity and for improving future projections. However, previous studies have primarily relied on observational analyses, and the capability of climate models to reproduce extreme TC intensity—especially during the pre-satellite era—remains poorly explored. As an example, the year 1959 represents one of the most extreme TC seasons over the western North Pacific (WNP), during which five Category-5 TCs occurred between August and October, accounting for 15.6% of all TC records, the highest on record.
Based on TC best-track data and reanalysis products, we show that both anomalous TC genesis locations and frequent rapid intensification (RI) events contributed to the exceptionally high basin-mean lifetime maximum intensity (LMI) in 1959. More TCs formed over the open WNP basin around 150°E, where storms tend to achieve higher LMI, while the number of RI events far exceeded the climatological mean. These features are closely linked to large-scale circulation anomalies, including an enhanced monsoon trough, a weakened subtropical high, and the eastward shift of tropical upper-tropospheric trough (TUTT). Together, these circulation changes modulated TC genesis positions and enhanced RI occurrences, ultimately leading to a higher basin-mean TC LMI.
To further investigate the role of sea surface temperature anomalies (SSTAs) and assess the reproducibility of this extreme season, we conducted a set of three-month ensemble simulations using the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) at 28-km horizontal resolution, with 10 ensemble members for each experiment. Four experiments were performed: a climatological SST experiment (CLIM), a realistic 1959 SST experiment (REAL), and two sensitivity experiments representing subtropical Central Pacific warming (CPW) and Indian Ocean warming (IOW), respectively. The REAL experiment successfully reproduces the enhanced TC intensity in 1959, along with the associated large-scale circulation anomalies, demonstrating the capability of NICAM to simulate historical extreme TC seasons. Sensitivity experiments reveal that CPW plays a dominant role in driving the extreme TC activity. The positive SSTA in the central Pacific induces a Matsuno–Gill–type response, generating anomalous low-level cyclonic circulation and upper-level anticyclonic circulation over the WNP. This response strengthens the monsoon trough and weakens the subtropical high, thereby shifting TC genesis locations, increasing RI frequency, and finally enhancing basin-mean LMI. In contrast, the IOW experiment shows a much weaker impact on both large-scale circulation and TC intensity.
These results highlight the critical importance of subtropical central Pacific SST forcing in shaping historical extreme TC seasons and demonstrate the value of high-resolution climate models in advancing our understanding of TC intensity variability.