During late August 2019, a major warming of the Southern Hemisphere (SH) stratospheric polar vortex commenced. By early September 2019, temperatures in the mid-to-upper stratosphere over the Antarctic polar cap reached all-time records for this time of the year. Prior to 2019, spring 2002 was the only time in the previous 40 years when we observed a dramatic major sudden stratospheric polar vortex weakening and warming event in the SH. The extraordinary 2002 event was the main driver of a significant rise of the total column ozone over Antarctica, a record strong negative index polarity of the Southern Annular Mode (SAM), and extreme hot and dry conditions over Australia in spring 2002. In contrast to 2002, when seasonal climate prediction models did not include the stratosphere, state-of-the-art international models including the Australian Bureau of Meteorology's dynamical seasonal climate forecast system ACCESS-S1 predicted this dramatic warming and weakening of the polar vortex from mid-August. The prediction for September was well verified with the rapid reduction of the zonal-mean zonal wind speed at the 10 hPa level at 60°S - from 86 m/s to 12 m/s within three weeks from mid-August to mid-September. This wind reduction was unprecedented by a large margin for that time of the year, and it was accompanied by an extraordinarily rapid increase of the planetary wave activities penetrating into the stratosphere from the troposphere, which was also never observed before in September.

In this presentation, we will discuss the evolution of this extraordinary major stratospheric vortex weakening event, and its impacts on the SAM and associated Australian springtime climate. We will also review the hindcast skill of the ACCESS-S1 forecasts to predict the stratosphere-troposphere coupling and the prospects for improved predictions in the future.