Summer was a season of extremes, with record hot days and drought in parts of central NSW contrasting with all-time high rainfall in tropical regions, the Australian Actuaries Climate Index reveals.

Its findings come as the Bureau of Meteorology’s winter climate outlook predicts a season that is warmer and drier than average for large parts of the country. It follows an autumn expected to be among Australia’s five warmest on record.

The Actuaries Climate Index details the hottest summer on record for both average temperature and frequency of extreme highs.

Data is collected nationally and grouped into 12 climatologically consistent regions. Each season is compared against previous years, back to 1980.

Meanwhile, the bureau says higher than average pressure is likely over southern and possibly eastern Australia this winter. This can keep cold fronts further south than normal, reducing winter rainfall to the southern states.

Bureau models show June rainfall is likely to be below average in NSW, Victoria, eastern SA and southern parts of Queensland and the NT.

A positive phase of the Indian Ocean Dipole is forecast to develop this month and persist until spring. Typically, this means below-average rainfall for much of central and southern Australia during winter and spring.

The bureau places the likelihood of an El Nino developing this year at about 50%, double the normal risk for this time of year. It says Australia’s climate patterns are also “influenced by the long-term increasing trend in global air and ocean temperatures”.