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

Abstract

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.

Compounding impact of severe weather events fuels marine heatwave in the coastal ocean

“…Several studies have shown that the presence of stratification prior to storm arrival can significantly reduce the intensity of impending storms, via aheadof-eye SST cooling 7,8,10,11 . Conversely, other studies have suggested or shown that anomalously warm conditions on shelves have contributed to the intensification of hurricanes through landfall 6,[12][13][14] .…”

Radial Distributions of Sea Surface Temperature and Their Impacts on the Rapid Intensification of Typhoon Hato (2017)

“…Note the period after 0000 UTC 23 August, when stronger LHF occurs in CPL storm eyewall with the even weaker tangential wind than FO storm. The local SST becomes higher in the CPL experiment ( Figure 10c) because of the TC induced hot onshore surface water [49]. This could further suggest the important role of local SST in modulating the energy source, and thus the inner-core evolution in storms.…”

“…To reproduce the ocean responses to the typhoon forcing, ROMS was coupled to WRF through the Model Coupling Toolkit (MCT). ROMS is a free-surface primitive equation ocean model in sigma vertical coordinate, which has been widely used in estuaries, coastal [48,49], and open ocean simulations [17,50] for both research and operational forecasting (model is developed and supported mainly by researchers at the Rutgers University, University of California Los Angeles, codes available at http://www.myroms.org). Configured with 30 vertical levels and one horizontal domain, the single domain of ROMS covered the same region as WRF did with the horizontal resolution of 18 km, which means that the variables could be transferred from grid to grid between two models.…”

Rapid observations of ocean dynamics and stratification along a steep island coast during Hurricane María

“…These results present a new framework for understanding how a stratified ocean may respond to TC forcing along steep coastal margins. Previous work has found three predominant coastal ocean baroclinic responses to TC winds during the initial forced stage: (i) cooling from shear-induced mixing ( 14 , 15 ), (ii) restricted cooling due to downwelling and offshore advection of cold bottom water ( 16 ), and (iii) warming due to downwelling circulation and suppression of upwelling ( 20 , 21 ). Our observations document a previously unidentified response, whereby offshore-directed TC winds along a relatively narrow insular shelf with a steep slope result in sustained, warm SSTs throughout the storm, despite the influx of increasingly cold waters at depth.…”