The Australian Community Climate and Earth System Simulator (ACCESS) has been adapted for operational and research applications on tropical cyclones. The base system runs at a resolution of 0.118 and 50 levels. The domain is relocatable and nested in coarser-resolution ACCESS forecasts. Initialization consists of five cycles of four-dimensional variational data assimilation (4DVAR) over 24 h. Forecasts to 72 h are made. Without vortex specification, initial conditions usually contain a weak and misplaced circulation pattern. Significant effort has been devoted to building physically based, synthetic inner-core structures, validated using historical dropsonde data and surface analyses from the Atlantic. Based on estimates of central pressure and storm size, vortex specification is used to filter the analyzed circulation from the original analysis, construct an inner core of the storm, locate it to the observed position, and merge it with the large-scale analysis at outer radii.Using all available conventional observations and only synthetic surface pressure observations from the idealized vortex to correct the initial location and structure of the storm, the 4DVAR builds a balanced, intense 3D vortex with maximum wind at the radius of maximum wind and with a well-developed secondary circulation. Mean track and intensity errors for Australian region and northwest Pacific storms have been encouraging, as are recent real-time results from the Australian National Meteorological and Oceanographic Centre. The system became fully operational in November 2011. From preliminary diagnostics, some interesting structure change features are illustrated. Current limitations, future enhancements, and research applications are also discussed.

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Rapid intensification of near-landfall tropical cyclones is very difficult to predict, and yet has far-reaching consequences due to their disastrous impact to the coastal areas. The focus for improving predictions of rapid intensification has so far been on environmental conditions. Here we use the Coupled-Ocean-Atmosphere-Wave-Sediment Transport Modeling System to simulate tropical cyclones making landfall in South China: Nida (2016), Hato (2107) and Mangkhut (2018). Two smaller storms (Hato and Nida) undergo intensification, which is induced by the storms themselves through their extensive subsidence ahead of the storms, leading to clear skies and strong solar heating of the near-shore sea water over a shallow continental shelf. This heating provides latent heat to the storms, and subsequently intensification occurs. In contrast, such heating does not occur in the larger storm (Mangkhut) due to its widespread cloud cover. This results imply that to improve the prediction of tropical cyclone intensity changes prior to landfall, it is necessary to correctly simulate the short-term evolution of near-shore ocean conditions.

An atmosphere-only model system for making seasonal prediction and projecting future intensities of landfalling tropical cyclones (TCs) along the South China coast is upgraded by including ocean and wave models. A total of 642 TCs have been re-simulated using the new system to produce a climatology of TC intensity in the South China Sea. Detailed comparisons of the simulations from the atmosphere-only and the fully coupled systems reveal that the inclusion of the additional ocean and wave models enable differential sea surface temperature responses to various TC characteristics such as translational speed and size. In particular, interaction with the ocean does not necessarily imply a weakening of the TC, with the coastal bathymetry possibly playing a role in causing a near-shore intensification of the TC. These results suggest that to simulate the evolution of TC structure more accurately, it is essential to use an air-sea coupled model instead of an atmosphere-only model.