Above average ocean temperatures leading to marine heatwaves have implications for many marine ecosystems and industries. The impacts felt include mass coral bleaching and mortality, altered aquaculture yields, changes in wild fish migration patterns, and marine ecosystem deterioration. Impacts are primarily related to marine heatwave severity and duration. Seasonal forecasts of marine heatwave risk covering timescales from weeks to seasons from dynamical ocean-atmosphere models can be very useful tools for marine managers, businesses and researchers. The Australian Bureau of Meteorology’s seasonal forecast model ACCESS-S2 currently produces operational real-time forecasts of sea surface and subsurface temperatures. In partnership with CSIRO, marine heatwave categorical and probabilities of exceeding the 90th percentile forecasts derived from subseasonal to seasonal timescales have been developed and are now operational. These new products will complement existing operational accumulated thermal stress forecast products developed for coral bleaching to improve both the understanding and the management of MHW events.