Fig. 1: Spatial and temporal tropical cyclone genesis frequency (TCGF; unit: count), and correlation with the controlling factors.

a North Atlantic (NA) TCGF anomaly in 2023 (shaded) and composite of TCGF anomaly for top four El Niño events (1982, 1987, 1997 and 2015; contour); (b) same as (a) but for the western North Pacific (WNP); (c) time series of NA TCGF from 1980 to 2023; (d) time series of WNP TCGF; (e) correlations between NA TCGF with respective reversed Niño [Niño\(\times\)(-1)], reverted Pacific Meridional Mode (PMM) index [PMM\(\times\)(-1)], tropical North Atlantic (TNA) index and multi-regressed (Reg) TCGF based on above three indices and the global warming (GW) index based on the 1980–2023 period; and (f) correlations between WNP TCGF with respective Niño, PMM, reverted TNA [TNA\(\times\)(-1)] index and multi-regression result for 1980–2023 period. The 2023 TC tracks in (a, b) are shown in green and purple colors that the green represents TC intensity is smaller than Category 1 (C1) while the purple means the intensity is above C1. The black contours in (a, b) stand for the composite of TCGF anomalies between positive and negative ENSO phases with positive values using solid lines and negative using dashed lines. The values range from −3 to 3 with zero line neglected. The green and purple bars in (c) and (d) represent the five strong El Niño years with the green bars representing low TCGF year while purple bars for high TCGF year. The “Reg” represents correlations between TCGF and multi-regressed TCGF based on TNA, PMM, ENSO and GW indices. Here, the green bars stand for correlation coefficients with the un-detrended TCGF while the purple bars are for the detrended TCGF.