The late arrival of winter has seen much of south-eastern Australia record an exceptionally mild June.
A lack of major cold fronts until the final week or so of the month meant night-time temperatures in many regions were at or near record levels of warmth, according to the Bureau of Meteorology.
The June results come as the bureau updated its fortnightly El Nino report on Tuesday, noting renewed signals indicating such an event may occur this year. El Nino years tend to bring warmer and drier than usual conditions for much of Australia.
Melbourne matched its record 2008-high average minimum for June of 9.8 degrees, or almost 3 degrees above the 158-year norm of 6.9 degrees. Maximums came in at 15.8 degrees compared with the long-run average of 14.1 degrees.
Victoria also posted its warmest ever January-June period for mean temperatures, while almost the whole state recorded mean temperatures very much above average in June alone.
Sydney last month had no days when the mercury failed to reach 15 degrees, compared with six in a typical June. The city also had 13 days of 20 degrees or warmer weather, compared with a long-run average of 13.
As reported by Fairfax Media, Sydney had its third-warmest June in records going back 155 years, with mean temperatures 2.2 degrees above average. As Melbourne, average maximums for the Harbour City were 2.7 degrees above normal, also giving Sydney its warmest first half of the year.
"Both maximum (+0.8 degrees) and minimum (+1.4 degrees) temperatures were above average for NSW during June, with particularly mild conditions along the coastal strip associated with well above-average sea surface temperatures," the bureau said in a statement, adding that statewide average rainfall was close to normal (+8.6%).
Tasmania also had a warm June, with monthly records set for average mean, minimum and maximums set at several site in the state’s north. Canberra, too, had a mild June, with only eight nights with sub-zero temperatures compared with a long-run average of 13 nights.
The rainfall picture was more mixed in June, with most of Victoria recording above average rain, Tasmania near-average falls, while Sydney’s rainfall has only about half the level in a typical June.
The near-term outlook has Melbourne expected days with maximums of 15-17 degrees over the next week, or about 1.5-3.5 degrees above average for July. In Sydney, the next week should also be warmer than average by about the same margin, with daily tops expected in the 18-20 degree range.
El Nino outlook
In a separate report, the bureau said surface temperatures in the tropical Pacific Ocean are "currently at levels typically associated with a weak El Nino", although atmospheric patterns remain neutral.
"However, over the past fortnight changes have occurred in the atmosphere that may be a response to the warm surface waters – the Southern Oscillation Index has dropped by over 10 points, and weakened trade winds have re-appeared," the bureau said.
"These changes would need to persist for several weeks in order for an El Nino to be considered established, and it remains possible they are simply related to shorter term weather variability," the bureau said, noting the chance an El Nino this year remains "at least a 70 per cent chance".
During El Nino years, waters in the central and eastern equatorial Pacific are anomalously warm compared to those in the west. One result is that trade winds tend to slow or reverse, and rainfall patterns shifted eastward away from Asia and Australia.
Australia’s mean temperatures have risen about 0.9 degrees over the past century as the global climate has warmed.
Comparing the past 15 years with the 1951-1980 period, the chance of a very warm month has increased five-fold and the frequency of very cool months had dropped by about a third, the CSIRO and the Bureau of Meteorology noted in their latest State of the Climate report released earlier this year.