Tropical Cyclone Debbie (2017) caused 14 fatalities and an estimated US$2.7B and was ranked as the most dangerous cyclone to hit Australia since TC Yasi in 2011. Debbie rapidly intensified just offshore to a category 4 system before making landfall near Airlie Beach. After landfall, Debbie recurved to the south, rapidly weakened into a tropical low, and finally merged with a cold front, causing significant flooding to Queensland and New South Wales. The Bureau of Meteorology operational forecast models did a relatively poor job of providing guidance to the forecasters, in part because of the unusual synoptic conditions that caused Debbie to stall for 24 hours before turning southwest toward the east coast of Australia. This, along with the high impacts caused after landfall, make TC Debbie a very good case to examine in more detail.    

In this presentation, we focus on the physical mechanisms associated with the heavy rainfall produced by Debbie as, and after it made landfall. To study the case, a high-resolution WRF simulation is used with 2-km horizontal resolution. The rainfall is characterised by two main stages: extremely heavy rainfall as the TC came ashore, and a secondary maximum near the NSW-QLD border as the TC interacted with a midlatitude cold front and became extratropical. In this presentation, the mechanisms associated with these rainfall events will be discussed in the context of the broader cyclone precipitation climatology.