"Around 50 per cent of the country had its highest on record mean temperatures," Karl Braganza, head of climate monitoring for the bureau, said. (See chart below.) Fire authorities made the most of dry conditions to have a busy controlled-burning season in many regions, including the Three Sisters area of the Blue Mountains. Credit:Dean Sewell The key influences for the abnormal heat were "the impact of the El Nino and the increasing temperatures due to global warming," Dr Braganza said. "You've just seen a spike in a lot of the global and regional indicators." With the El Nino now ended in the Pacific, temperatures should drop back closer to their long-term averages in June, he said.

For residents in Sydney and Melbourne, a cool end to May took the edge off the balmy conditions. Even so, the Harbour City recorded its second-warmest May on record for maximum temperatures, while Melbourne's temperatures were between 1-2 degrees warmer than average. For Sydney, autumn was a full 0.4 degrees warmer than the previous hottest mark for the season, set in 2014. There were numerous other records set, including the most nights above 12 degrees, which stretched 232 nights. Unusually warm conditions persisted in much of Australia through most of autumn. Credit:Kirk Gilmour The near-term outlook remains on the warm side, with Sydney's tops over the next week expected to range from 18-21 degrees compared with the June average top of 17 degrees. Melbourne's forecast tops of 16-17 degrees are also above the city's June average maximum of 14.1 degrees, the bureau said. A March heatwave helped ensure the prolonged summer continued well into autumn, Dr Braganza said.

May itself was the second-warmest on record for Australia, with mean temperatures1.88 degrees above the long-run norm, trailing only May 1958, the bureau said. (See chart below.) Rainfall was much closer to average for both autumn and May for much of the country. For NSW, which had its hottest autumn on record, rainfall was about 29 per cent below average. Last month made up for much of the deficit, though, with the state recording its wettest May since 2000 with rainfall up by about one-sixth compared with the average.

Coastal NSW missed out on a lot of the rain in both the autumn and May, with Sydney particularly dry last month. The city had its fifth-driest May on record, with just six days of rain. (See chart below.) The dry conditions allowed fire authorities to have one of their most productive seasons for controlled burning in recent years. For Victoria, rainfall in autumn was close to average with temperatures easily the warmest on record. Mean temperatures were 1.88 degrees above average, beating the previous warmest autumn in 2007 when the anomaly was 1.49 degrees. Last month was the state's wettest May since 1995, with totals about one-third above normal. Nationally, the past 12 months have been the second warmest on record for mean temperatures, just behind the period from November 2012, Dr Braganza said.

"When you look at sea-surface temperatures around Australia, for instance, the record isn't just by a little bit - there's a real spike in the graph," he said. (See chart of March temperatures below.) Record warm sea temperatures stretched along Australia's north and also around Tasmania in March and April, the bureau said. The record warm waters have been blamed for causing coral bleaching across much of the Great Barrier Reef and also north-western Australia. As much as one-third of the corals off northern Queensland are dead or dying. Australia's conditions have been largely in sync with global temperatures, which have set record monthly highs for each of the past 12 months.

This year will "be up there" with last year's record global temperatures after such a warm start to the year, Dr Braganza said.