Review of Australian east coast low pressure systems and associated extremes.

Intense cyclones often result in severe impacts on mid-latitude coastal regions of southeastern Australia, including those due to associated natural hazards such as extreme winds, ocean waves, storm surges, precipitation, flooding, erosion, lightning and tornadoes in some cases. These low-pressure systems, known as east coast lows (ECLs), have been examined in a wide range of different studies, with considerable variations between such studies in what they consider to be an ECL, and their findings on the characteristics of these storm systems. Here we present reviews of literature and other information such as operational forecasting approaches, which are then used to produce a comprehensive synthesis of knowledge on ECLs and associated weather and ocean extremes. This includes aspects such as their definition, formation, meteorology, climatology and drivers of variability from short-term weather time scales up to long-term historical climate trends and future projec- tions. Australian ECLs are also considered here in relation to similar phenomena from other regions of the world. A defini- tion based on this synthesis of knowledge is as follows: ECLs are cyclones near southeastern Australia that can be caused by both mid-latitude and tropical influences over a range of levels in the atmosphere; Intense ECLs have at least one major hazard associated with their occurrence, including extreme winds, waves, rain or flooding. Knowledge gaps are examined and used to provide recommendations for future research priorities. This study is intended to lead to improved guidance and preparedness in relation to the impacts of these storms.

Figure 1. Cyclone activity near eastern Australia, showing the annual mean number of low-pressure system events (per 5° × 5° region) based on applying a tracking method for MSLP and 500 hPa geo- potential fields from the ERA-Interim reanalysis from 1979 to 2009 [as described in Pepler et al. (2015)]. Also shown are coastlines of Australia and New Zealand (to the southeast), with latitude and lon- gitude, names for maritime regions as well as Australian states of Queensland (QLD), New South Wales (NSW), Victoria (VIC), Tas- mania (TAS), South Australia (SA) and Northern Territory (NT)