This study examines the unique annual cycle characteristics of tropical cyclone (TC) genesis in the South China Sea (SCS). In contrast to the TC bimodal structure in the Bay of Bengal (BoB) and its unimodal pattern in the Northwestern Pacific (WNP), the SCS exhibits a distinct step-like pattern with two jumps—the first occurring from April to May and the second from July to August, with the flat condition during May–June–July. Hence, TC in SCS witnesses the surprising transition between BoB and WNP. To investigate the underlying mechanisms, the genesis potential index is applied for a quantitative assessment of large-scale environmental factors. Results indicate that in the SCS, the mid-level atmospheric relative humidity is the dominant factor driving the first TC genesis jump in May, whereas the vertical wind shear contributes to the second jump. In the WNP, the mid-level atmospheric relative humidity remains the most crucial for TC peak feature. This study advances our understanding of the unique annual cycle of TC in the SCS in comparison with the neighboring BoB and NWP, offering valuable insights to improve the forecasting skills in the region.
Observations from the Little Bunker
Last updated: October 16, 2025 04:11 AM
Atmospheric CO₂
424.4 ppm
+18.2
ppm/year
Atmospheric CH₄
1933.54 ppb
+12.29
ppb/year
Global Temperature
+1.48 °C
Peak: +1.73°C
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8.1 billion
+67
million/year