The simulations of summers (DJFs) of anomalously high surface temperatures by the Australian Community Climate Earth-System Simulator – Seasonal (ACCESS-S1) are evaluated using hindcasts between 1990 and 2012. A percentile-based method with the top quintile (i.e., above 80%) of the daily maximum surface temperatures is used to determine the hot seasons for both model output and Australian Water Availability Project (AWAP) observations for comparison. The study is conducted over the Australian continent (AUS) as well as 4 sub-regions, namely southeast (SE), southwest (SW), northeast (NE), and northwest (NW) separated by the 25^oS latitude and 135^oE longitude boundaries.

The analysis on the observations indicate that the hot summers defined over all of Australia (AUS) have different underlying causes than those defined over the SE sub-region only. The AUS hot summers are mostly connected to ENSO whereas the SE hot summers show clear signatures of the negative phase of the Southern Annular Mode (SAM) and synoptic weather dynamics associated with anomalously high rainfall in Northern Australia. ACCESS-S1 fails to differentiate these regional signatures, relying mostly on ENSO regardless of the region when simulating hot summers. ACCESS-S1 does, however, resolve the synoptic dynamics and the SAM teleconnection to hot summers with a significantly weaker intensity. These shortcomings of ACCESS-S1 leads to problems in representation of summers of extreme heat especially in terms of precipitation failing to simulate rain in northern Australia connected to the heat extremes over southeast.