The impact of sea surface temperatures over the Coral Sea on the warm core intensification of a Tasman Sea cyclone

Abstract In early June 2016 a large rainband with an embedded subtropical cyclone brought extensive heavy rainfall along Australia's east coast from southern Queensland to Tasmania. In the lead‐up, sea surface temperatures (SSTs) in the Coral and Tasman Seas were the warmest on record for the time of year. This study uses convection‐permitting simulations with different SST configurations to assess their influence on cyclone development. Simulations with observed SST – both fixed (Control) and daily evolving (Evolving) – produce a stronger cyclone off the New South Wales (NSW) coast compared with a simulation using 3 June climatological SST (Climatology). The cyclone also stalls longer near the NSW coast in the observed SST runs. Smoothing a prominent warm eddy (Smooth) and replacing the Tasman Sea SST with climatological SST (Tasclim) has little effect on cyclone intensity. Replacing Coral Sea SSTs with climatological values (Corclim) yields a weaker cyclone off the NSW coast, similar to Climatology and it intensifies later and farther south. These results indicate that the anomalously warm Coral Sea SSTs played a key role in cyclone intensification off the NSW coast, despite peak intensity occurring over the Tasman Sea. The greater cyclone intensity and slower southward movement over the Tasman Sea resulted in stronger and more prolonged onshore winds along the southern NSW coast, increasing the potential for coastal damage. At NSW latitudes, the intensified cyclone in Control, Evolving, Smooth, and Tasclim is associated with the formation of a warmer lower‐tropospheric storm core, which develops more prominently when the Coral Sea SST is elevated. These findings highlight the critical role of the Coral Sea's warm SST as a driver of the cyclone's development and intensification in this event.