Just another Tasman Sea marine heatwave?

Through late November and early December 2023, a severe category marine heatwave (MHW) was detected moving southwards off the east coast of Tasmania, Australia. The MHW was characterised by offshore sea surface temperature anomalies ~4^oC above climatological values embedded within and around large anticyclonic eddies with warm anomalies to >1000m depth. Given the deleterious impacts from previous MHWs on marine ecosystems, fisheries, and aquaculture in the region, serious concerns were raised. To advise and prepare stakeholders, a series of online briefings was given by physical, biogeochemical, fisheries, and social scientists on the current and likely evolving environmental conditions associated with the MHW. So, how unusual was this event? Was it successfully forecast? Was it expected from our knowledge of large-scale modes of climate variability and their teleconnections? This presentation will discuss the characteristics, evolution – both forecast and projected – and emerging impacts of the November-December 2023 Tasman Sea MHW. It will be argued that the characteristics of this event mirror expectations from anthropogenic climate change, and that initialised seasonal SST forecasts were little different from expectations under climate change projections and trend persistence.