Expectations of a strong El Nino weather event in the Pacific are being pared back but warmer-than-usual conditions are expected to persist, meteorologists say.
The latest prediction by the Bureau of Meteorology retains the 70 per cent or more likelihood that an El Nino will form this year with sea-surface temperatures in the equatorial central and eastern Pacific remaining well above average.
So far, though, there are few signs that the atmosphere is responding to the oceanic priming, suggesting that if an El Nino forms it is less likely to be as strong as some models were indicating earlier this year.
With typical El Ninos, the eastern Pacific is warm relative to the west, reversing or stalling the easterly trade winds. During such events, much of Asia and Australia have relatively dry and warm years, while the Americas often have wet years.
One aspect that is intriguing scientists is the fact that much of the Pacific – not just the east – is unusually warm. In fact, June may have experienced the largest departure in sea-surface temperatures of any month on record, climatologists say.
Japan Meteorological Agency noted this week that monthly sea-surface temperatures were ''remarkably'' above average in regions ranging from near Japan to the coast of North America, and from Mexico to the Philippines.
Global average surface temperatures – including land and near-surface readings – were 0.32 degrees above the long-term average, making last month the hottest June in records going back to 1891, JMA said, citing preliminary figures.
If June is the hottest month, it would add to the warmest May and the equal warmest April, increasing the likelihood that 2014 will top 2005 and 2010 as the warmest year on record.
The fact the El Nino-like conditions in the ocean are waiting for the atmosphere to respond is one reason for the recent warmth.
The release of ''stored heat is helping to warm up the global atmosphere'', Andrew Watkins, manager of Climate Prediction Services at the Bureau of Meteorology, said. "It's not unexpected that these months have been so warm given the amount of heat that must have come out of the Pacific."
Meteorologists are also watching the Indian Ocean, where warmer-than-usual conditions in the east are helping to stall the development of an El Nino. One benefit of unusual warmth in this region is that moisture is streaming over the Australian continent, bringing much needed rain to south-eastern parts.
Central western and south-western NSW had their best rains this week in three months and more is on the way, according to Weatherzone.
Sydney, though, will probably see another week of above-average maximum temperatures and little rain – continuing a trend of the past month and longer.
Friday will be the coolest day, with a maximum of 17 degrees, but other days should have tops of 18-21 out to next Wednesday, the bureau said.
'On its way'
Max Gonzalez, a senior meteorologist at Weatherzone said that while some Pacific waters had cooled off lately, sub-surface temperatures were as much as 3 degrees warmer than normal in parts of the centre and east.
“The strength of the event may not be as strong as we are thinking a couple of months ago but an El Nino is still on its way," Mr Gonzalez said.
The bureau's Dr Watkins said computer modelling suggested an El Nino effect is still likely, although not until later in the year than earlier thought.
A bout of westerly winds a fortnight ago hinted at the atmosphere coupling with the ocean to reverse the trade winds and reinforce El Nino conditions, but things then settled back to normal.
"It's starting to pick up a little bit again," Dr Watkins said, with meteorologists studying the persistence of weakening of the trade winds. "We're still in that waiting phase" to see whether the event is a short one or more prolonged.
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