A computationally inexpensive operational wave forecasting system taking wave‐current interactions over the fast‐flowing Agulhas Current into account is explored. Spectral wave model hindcasts at 1/16 of a geographical degree are employed using the Simulating Waves in the Nearshore (SWAN) wave model. Unidirectional wave‐current coupling, with currents affecting waves, is performed using both Operational Mercator 1/12 degree (ORCA12) and GLOBCURRENT 1/4 degree currents. Comparisons between the coupled and uncoupled simulations indicate that wave amplification or lowering is highly dependent on the current magnitude and wave incident angle. In opposing current scenarios, the significant wave height can increase by 20–40% and by 60% in extreme cases. Model validation is performed using Jason‐3 satellite altimetry measurements and in situ directional wave buoy measurements. The nearshore wave directional dispersion is found to be significantly influenced by the core of the Agulhas Current. This is especially prominent in current‐following cases with wave‐current direction differences of up to 20°. The findings are all corroborated by simplistic, idealized models.

Heavy rainfall occurs frequently on the subtropical eastern seaboard of Australia (ESB). Many rainfall events are associated with slow‐moving, upper‐level low‐pressure systems. Combined with moisture‐rich easterly winds associated with a surface anticyclone, these systems can produce heavy rainfall, leading to flooding events. Although the general meteorology of these events has been documented, much of the focus has been on surface processes, with limited attention paid previously to the dynamics aloft. Here, we investigate the upper‐level dynamics associated with heavy rainfall events over the ESB with the use of a coherent potential vorticity (PV) minimum climatology on the 330‐K isentropic level. Slow‐moving coherent cyclonic PV anomalies produce more rainfall than fast‐moving anomalies over the ESB. Rossby‐wave breaking is responsible for the development of a slow‐moving coherent cyclonic PV anomaly as well as the commonly observed surface patterns that are necessary for heavy rainfall over the ESB. Slow cyclonic coherent PV anomalies are either transported equatorwards into the Tropics, where they may influence tropical weather systems, or removed from the region by the restoration of the subtropical jet over continental Australia.

Regional storm tidal levels of the South African coastline are investigated by means of a calibrated and validated numerical model. The model was developed utilizing the shallow water hydrodynamic model, Delft3D. This model was coupled (online) with a non-stationary spectral wave model (developed in the Simulating WAves in the Nearshore (SWAN) numerical code). A local, 4.4 km version of the Unified Model was applied as atmospheric forcing for the coupled system. The models presented in this study form part of the operational marine forecasts of the South African Weather Service, Wave and Storm Surge model. The operational protocol and model calibration and validation are presented via statistical correlations with measured water levels at six South African coastal locations. The main calibration parameters and thus physical drivers were winds, atmospheric pressure and waves. The validated numerical model is used to provide an experimental physical description of South African storm surge characteristics, per coastline. The dominant driver of South African storm surge is winds associated with mid-latitude cyclones. Further novelty in the present study is the quantification of the relative contribution of extreme storm wave set-up to the South African storm surge signal. This wave set-up contributes approximately 20% of the total surge signal in the southwest, with winds contributing approximately 55%. The importance of the continental shelves is also elucidated concerning the frictional shoaling effects of the long surge wave propagation.

Antarctic sea ice is prevalently seen as a major player in the climate system, but it is also an important factor in polar maritime safety. Remote sensing and forecasting of Southern Ocean sea ice at time scales suitable for navigation and research planning remain challenging. In this study, numerical sea ice drift forecasts are assessed from the perspective of informing shipping operations. A series of tests is performed to ascertain whether an operational global ocean and sea ice model and a simple free-drift model can provide accurate drift estimates over short lead times. Both approaches are evaluated against ice drift measurements from buoys deployed during two research cruises in the Southern Ocean marginal ice zone during winter and spring. The numerical forecast model was able to forecast sea ice trajectories over 24 h with an average position error of 16.6 km during winter and 9.2 km during spring. The simpler free-drift model, using empirically optimised wind scaling, returned an average position error of 15.9 and 9.3 km during winter and spring respectively. Model skill for both the dynamical and free-drift models is lower in winter than in spring. Free-drift model skill appears linked with sea ice consolidation, which may assist in determining when and where this approach is fit for purpose. Lingering uncertainties regarding the rheological representation of sea ice in the dynamical model and the quality of the wind and ocean forcing remain, potentially affecting model skill over tactical navigation time frames.