Warmth continues to build in the Pacific Ocean. Photo: Kate Geraghty

The powerful El Nino continues to intensify in the Pacific and is now the strongest since the record-breaking 1997-98 event, the Bureau of Meteorology said.

Weekly surface readings in a closely watched Pacific equatorial zone known as Nino3.4 exceeded 2 degrees at the end of August for the first time since 1997-98, the bureau said in its fortnightly update.

John Vanston on his property near Bridgewater, Victoria, earlier this year. Climatologists say 2015 is likely to exceed 2014 as the hottest year on record. Photo: Justin McManus

"You're looking at a significant event in anyone's books," Andrew Watkins, the bureau's manager of climate predictions, said.

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The atmosphere and the ocean "are fully coupled", reinforcing each other to strengthen the event, the bureau said.

The current record-setting trio of category 4 strength hurricanes in the Pacific are helping to reverse the easterly trade winds that typically blow along the equator, allowing more heat to build up in the east, Dr Watkins said.

Water temperatures at a depth of 75 metres in regions of the far eastern Pacific are now more than seven degrees warmer than normal.

On current model projections, the El Nino is expected to plateau in coming months but linger to as late as next May, the bureau said:

El Ninos typically start to influence rainfall over eastern and southern Australia during the late winter into spring.

During the winter that ended on Monday, national rainfall was 16 per cent below the long-run average, the bureau said in a separate report. Temperatures were 0.83 degrees above average for maximums, making it Australia's equal eighth warmest winter on record.

Record warmth in parts of the Indian Ocean has helped to moderate the El Nino impacts so far, particularly across much of NSW. Most of Victoria, though, had a particularly dry winter, the bureau said:

The odds favour a wetter-than-average spring for parts of inland western Australia but remain mixed for most of the rest of the country, Dr Watkins said.

Evidence of cooling temperatures in the waters south of Sumatra in Indonesia will be watched particularly closely to see if they spread further down the coast of WA, reducing the likelihood of moist air steaming across the continent.

As the bureau noted last week in its spring outlook, water reservoirs in some key areas are already down on last year.

While Australia may have dodged major impacts of the El Nino so far, fire authorities are bracing for elevated fire risks over the summer in most of the populated regions of southern Australia.

Other countries, such as the island nations of the South Pacific and Papua New Guinea are already experiencing drought conditions.

With such a large area of the Pacific much warmer than average, surface temperatures globally are running at record levels as the El Nino combines with background warming from climate change.

Climatologists say 2015 is now highly likely to exceed 2014 as the hottest year on record and 2016 could be warmer again given the momentum in the world's oceans.