Extensive and Prolonged Cooling Effects of Tropical Storm Pabuk on the Southern South China Sea

Abstract

In January 2019, Tropical Storm Pabuk traversed the southern South China Sea, inducing significant upper-ocean cooling with a maximum temperature drop of 3.8°C lasting over three weeks. As the storm passed directly over the Bailong marine meteorological buoy (5.843°N, 104.208°E), high-frequency oceanic and atmospheric observations captured its immediate impact, providing valuable insights into air-sea interactions during extreme weather events. Analysis of buoy data and FIO-COM simulations reveals that Pabuk triggered a rapid sea surface temperature (SST) decline, initially driven by wind-driven vertical mixing and heat flux loss, followed by prolonged cooling sustained by cold advection. The latter was primarily controlled by changes in the Vietnam Coastal Current (VCC), whose intensity and structure were significantly altered by the storm. Additionally, near-inertial oscillations (NIOs) enhanced subsurface mixing contributing to the persistence of cooling, whereas winter monsoon winds further influenced post-storm SST evolution. The cooling response exhibited strong spatial variability: in deep offshore regions, vertical mixing dominated, entraining colder subsurface waters into the mixed layer; along the Vietnam coastal shelf, cold advection played a leading role; in shallow waters, heat flux loss initiated cooling with residual cold advection and NIO-driven subsurface mixing extending SST anomalies. These findings underscore the heightened sensitivity of shelf seas to tropical storms, where coastal currents, wind-driven mixing, and bathymetric constraints critically influence SST evolution. A more accurate representation of these localized processes in oceanographic and climate models is essential for improving storm impact assessments and upper-ocean thermal predictions.