The Bureau of Meteorology's monthly reports showed average maximum temperatures were 2.62 degrees above the long-run average, beating the previous record set in 1975 by a full two-thirds of a degree.

Even with widespread overnight frosts, mean temperatures - averaging out day and night time temperatures - came in as the third highest for July in records dating back to 1910.

The bureau confirmed Sydney had its second-warmest July for maximums, with an average daytime top of 19.1 degrees, or 2.7 degrees above the norm.

In the city, 10 days exceeded 20 degrees during the month, or more than triple the long-term average of such days. The cool nights kept minimum temperatures generally below par.

Rainfall in the city was the least since 1995, with less than one-seventh the typical falls at 12.6 millimetres.

NSW as a whole posted its driest July since 2002, with rainfall totals 70 per cent below average. Daytime temperatures were also the second-warmest on record. All but four days in the month were warmer than normal for maximums, the bureau said.

Dominant high-pressure systems have limited the penetration of rain-bearing cold fronts beyond the southern coast for most of the past two months, with little sign of the pattern breaking up.

A similar story was true south of the border, with Victoria marking its second-driest start to winter in more than a century of records. June-July rainfall totals are the lowest for any year except 1982, backing up its record dry June.

After a cool start to July with several stations in Melbourne registering their coldest nights since 1997, temperatures in the city were generally warmer than average, particularly towards the end of the month.

As the bureau chart below shows, most of Australia posted very much above or record warm daytime temperatures last month.

"Average maximum temperatures were the highest on record for July over large parts of Queensland, Northern Territory and the northern half of Western Australia, with all three regions recording their warmest July days on record as a whole," the bureau said.

Queensland's warmest July on record for maximums beat a record set in 1915, while the NT's tally beat the previous record notched in 1975 by 0.84 degrees.

While the first half of July was particularly frosty for parts of inland regions - with some southern NSW and Victorian sites recording their coldest nights - overall minimum temperatures came in 1 degree warmer than usual for the month.

The monthly anomaly for maximum temperatures while large for July is not unprecedented, Blair Trewin, senior climatologist with the bureau, said. Other big jumps in setting recent record maximums include the 1.13-degree leap for August 2009 and 0.91 degrees in September 2013.

Rain in short supply

Nationally, Australia averaged 13.5 millimetres of rain, 39 per cent below average.

The Murray-Darling Basin, a key foodbowl region, reported another poor month, with rainfall less than half the average.

As the bureau chart below shows, the largest rain anomalies were across southern Australia, while the NT recorded some out-of-season rain.

The bureau's outlook for August-October indicates the odds favour continuing warmer and drier than average conditions across southern Australia.

Climate influences

The unusual dry spell for southern Australia is not being driven by conditions in the Pacific or the Indian Ocean.

As the bureau noted on Tuesday, the El Nino Southern Oscillation used to track pressure differences across the Pacific remains in its neutral phase, and all of the eight models the agency uses predict it will remain so for the rest of 2017.

Similarly, most models forecast the Indian Ocean Dipole, which tracks relative temperatures across that ocean, will remain in neutral for the key winter-spring period.

Of greater importance has been the westerly wind belt, which has contracted towards Antarctica. During so-called positive phases of the Southern Annular Mode, cold fronts track further south as has been the case in recent months.

As a result, rain bands have tended to skirt key farming regions of south-west and southern Australia in a pattern that models forecast will become more common as the climate warms, the bureau has said.