Sub-synoptic scale features associated with extreme surface gusts during the South Australia Storm of September 2016-Part I: characteristics of the event

Winds are one of the major meteorological contributors to deaths, damage and insured losses in Australia. A 'freak storm' hit the state of South Australia on 28 September 2016, causing state-wide blackouts and leaving 1.7 million people without power. In the first part of this two-part study, we analyse this event and find that it was indeed extreme, deepening more explosively than all but two Adelaide-affecting extratropical cyclones over the past 37 years and exhibiting the lowest central pressure. This generated hurricane force winds, with the central South Australia site of Neptune Island recording a gust of over 120kmh(-1). We show that this storm potentially contained a sting jet. Such jets are well known as a cause of major damage across Europe, and this is the first study which investigates whether a sting jet can be produced over Australia. The main deepening of the system occurred over the Great Australian Bight, so if a sting jet did form and make it to the surface, it was not the cause of the state-wide damage. However, the cyclone did contain numerous extreme gust-producing mesoscale features, as explored in part II of this paper (Earl and Simmons, 2018).