UC San Diego

A typical El Niño event often results in suppressed tropical cyclone (TC) genesis frequency (TCGF) over the North Atlantic (NA) and a distinct northwest-southeast dipole pattern in TCGF anomaly over the western North Pacific (WNP). The 2023 saw a strong El Niño event but surprisingly active NA and suppressed WNP TC activities. Here, we present that these unprecedented deviations were driven by the record-warm NA, a record-breaking negative phase of the Pacific Meridional Mode (PMM), and background global warming. Results from high-resolution global model experiments demonstrate that extraordinary Atlantic warming dominated the increased NA TCGF and contributed equally with the PMM to the suppressed WNP TCGF, overshadowing El Niños impact. Global warming also contributed to the observed TCGF anomalies. Our findings demonstrate that the typical influence of strong El Niño events on regional TC activity could be markedly altered by other climate modes, highlighting the complexity of TC genesis in a warming world.