Typhoon conduciveness of a semi-enclosed sea in the North West Pacific

Climatologically, the Bohai Sea, a semi-enclosed sea in the northwestern Pacific Ocean, has contributed minimally to typhoon hazards due to its low sea surface temperatures, high sea level pressure, weak vorticity, and landlocked basin. However, with rising sea surface temperatures and the poleward migration of typhoons in the northwest Pacific, a northward shift in typhoon intensity is evident from the increased frequency and energy of typhoons in the Bohai Sea. This study examines the typhoon climatology and triggering factors in the Bohai Sea from 1980 to 2020 and compared them with other Pacific basins. The analysis reveals the key factors including the strengthening of the Interdecadal Pacific Oscillation, rising sea surface temperatures, and weakening vertical wind shear during typhoon season potentially favoring the typhoon frequency and power in this basin. A paradigm shifts in the maximum potential intensity, with a 20-30% increase over the past four decades, suggests that the Bohai Sea is becoming more conducive to typhoon activity. Additionally, a 26% relative increase in typhoon size aligns with the increased latent and sensible heat fluxes in this basin. corelate the intensification and expansion of typhoons. Mathematical models of typhoon wind parametric field reveal that typhoons in the Bohai Sea are becoming more compact in the core and wider in the periphery, attributed to increasing central pressure drops and rising sensible heat fluxes.