The bureau’s latest temperature and rainfall outlooks for July to September released on Wednesday indicate that maximum temperatures have at least a 60 per cent chance of being warmer than average nationwide. Eastern Australia, including most of the Victorian, NSW and Queensland coast, has an 80 per cent or higher chance of warmer than normal days.

Minimum temperatures should also be warmer than average although the bureau notes the accuracy of models is “patchy” for most of the country for overnight conditions.

Areas of Australia still enduring rain deficiencies, such as northern NSW and much of inland Queensland, can expect a drier than average July-September period.  Odds favour closer to average rain for most of the rest of the country, although eastern Tasmania and the Top End may get more rain than normal.

An El Nino weather pattern has been brewing in the Pacific for months, creating conditions tilting towards drier and hotter weather for eastern and southern Australia. During El Nino years, waters in the central and eastern equatorial Pacific become unusually warm, particularly in comparison to waters in the west, with rainfall tending to shift eastwards away from Australia.

“Warming of the tropical Pacific Ocean over the past several months has primed the climate system for an El Niño in 2014,” the bureau said in a statement.

The Bureau noted, however, that the increase in ocean temperatures “has levelled off in recent weeks”.

“Despite some easing in the model outlooks, international climate models surveyed by the Bureau still indicate El Niño is likely to develop by spring 2014,” it said.

Despite this week’s blast of cold weather across south-eastern Australia, most of the country has been warmer than average.

Up to the end of May, Sydney and Melbourne recorded their third-warmest mean temperatures in records going back to 1910, with anomalies of 1.01 and 1.7 degrees, respectively.

Nationwide, the first five months have been the fifth hottest on record. By state, Queensland has had its warmest January-May period, with Victoria and South Australia their second warmest and NSW its third, according to the bureau.

Wild and warm weather

Emergency crews continue to clean up after Tuesday's combination of a cold front and intense low-pressure triggered gale-force winds across much of south-eastern Australia.

Parts of coastal Melbourne were inundated by surging waves and winds that exceeded 100 km/h in some places. Sydney had winds of 80 km/h or more, bringing down trees, with another bout of gusts of as much as 60 km/h expected later on Wednesday.

Another strong cold front is likely bring a wintry chill to both cities by the weekend.

Even so, Sydney and Melbourne will post another month of well-above usual warmth for June following a mild autumn that broke records in many parts of Australia.

Globally, temperatures are on the warm side too, with last month declared this week by the US National Oceanic and Atmospheric Administration to the warmest May over records dating back to 1880.

Karl Braganza from the Bureau of Meteorology's climate monitoring unit said it is "not entirely surprising" record temperatures are being set given that an El Nino is brewing in the Pacific.

"Global mean temperatures respond to the phase of the (El Nino-Southern Oscillation) cycle, and the Pacific either draws down heat from the atmosphere, or in effect releases heat to the atmosphere," said Dr Braganza.

"Currently the Pacific is not acting as a heat sink."

El Nino uncertainty

Dr Braganza, though, stressed the bureau's current forecast of a 70 per cent chance of an El Nino implies that such an event is not guaranteed.

While sea surface and sub-surface temperatures are unusually warm in the central and eastern Pacific - signals that indicate an El Nino is possible - a so-called coupling with the atmosphere that reinforces the process is yet to happen.

”If you don’t get that atmospheric push in the next two to three months, the system may start to change phase,” he said.

Predictions are also made complex by an unusual pattern being observed in the western Pacific where sea-surface temperatures are not trending the way they might be expected to in an El Nino year.

“What we’ve got is persistent anomalously warm waters (in the west) which is more typical of what you’d see in a neutral or weak La Nina year," Dr Braganza said. "It’s an interesting pattern at this time."