Flash drought is a term and concept that has gained increasing attention in the research literature and media since it was first coined in the United States in the early 2000s to describe a drought that has undergone a rapid intensification. In Australia the term has recently been used to refer to the 2017/18 drought in eastern Australia. For flash drought to occur, more than just a precipitation deficit, which is a common feature of all droughts, must occur. High temperatures, low humidity, strong winds, and sunny skies can all work together to produce rapid drought intensification, whose impacts will likely occur too quickly for many of the usual drought-coping mechanisms to be deployed. This study proposes the use of the Evaporative Stress Index (ESI), the standardized anomaly of the evapotranspiration to potential evapotranspiration ratio, to identify flash drought in Australia computed from the Bureau of Meteorology's land surface water balance model AWRA-L daily outputs. The case study of the January 2018 flash drought in eastern Australia is used to assess and demonstrate its suitability. Results show that the ESI accurately highlighted the event and offered potential for flash drought pre-warning by up to one month. In addition, the availability of long term and high resolution outputs from AWRA-L offers the ability to investigate multiple flash drought events in detail for greater understanding and to inform stakeholders.