Coastal Ocean Response and Its Feedback to Typhoon Hato (2017) Over the South China Sea: A Numerical Study

The coastal ocean response and feedback to Typhoon Hato (2017) were studied based on high-resolution numerical simulations using both a coupled and an uncoupled cloud-resolving model. As a category 3 landfalling typhoon that moved west-northwestward across the northern South China Sea, Hato (2017) rapidly intensified prior to its landfall and induced significant impacts on the coastal water column, causing warm and cold patches in sea surface temperature (SST) over the continental shelf to the right of the track. This feature was well captured in an air-sea coupled model experiment. The coastal SST warming was found to be related to a two-layer oceanic circulation across the continental shelf forced by the onshore surface wind stress to the right of the storm track. The associated onshore surface currents imposed a warm temperature advection and downwelling, leading to the SST warming in the inner sea shelf, as diagnosed from an ocean temperature budget analysis. A sensitivity experiment, in which the typhoon vortex was removed from the initial conditions, further confirmed that it was the strong onshore wind stress to the right of the storm track that forced the onshore surface currents and the SST warming in the inner sea shelf. Results from an atmosphere-only model experiment with the typhoon-forced coastal warm SST anomalies removed demonstrate that the typhoon-induced coastal warm SST anomalies contributed partly to the rapid intensification of Typhoon Hato prior to its landfall over South China and also slowed down the weakening of Hato at and shortly after its landfall.