Analysis of the Rainfall Mechanisms in Two Landfalling Tropical Cyclones

Tropical Cyclone Oswald (2013) and Debbie (2017) are considered to be two of the highest impact storms to make landfall in northern Australia. Oswald was a weak category 1 TC, but after making landfall in the far northern tip of Australia, Oswald turned southward just inland of the Queensland coastline, and lasted for more than 8 days over land. It produced over 1000 mm of rain in some areas causing flooding throughout eastern Queensland and into NSW with 6 fatalities and a total estimated US$2.28B in damages. As it moved southward, Oswald was able to reorganise and intensify over land, and then interacted with two upper-level trough-jet systems in the mid-latitudes. By comparison, 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. Debbie caused 14 fatalities and an estimated US$1.85B, making it the deadliest cyclone to hit Australia since TC Tracy in 1974.

Although the intensity and evolutional characteristics of Oswald and Debbie are very different, they both caused extreme rainfall and catastrophic flooding to the eastern coastal area in Australia. Furthermore, both TCs were relatively poorly forecast by the Bureau of Meteorology prediction models making them very good cases to examine in more detail. In this presentation, the rainfall characteristics of the two TCs are investigated using high-resolution WRF simulations with a series of sensitivity tests.