The El Nino climate pattern building in the Pacific is on track to be one of the strongest on record, with recent cyclones likely to intensify the event, the Bureau of Meteorology said.

Sea-surface temperatures in the central equatorial Pacific in June recorded the second largest anomalies on record for the month, behind only the June 1997 reading during the super 1997-98 El Nino event, the bureau said in its latest update.

Weekly sea-surface temperatures (see below) were also more than 1 degree above average for each of the regions monitored, their warmest sustained values since the 1997-98 event.

A string of tropical cyclones, including the rare July southern hemisphere storm, Cyclone Raquel, mean the El Nino will likely strengthen in coming weeks as "a strong reversal of trade winds" near the equator takes place.

"This is likely to increase temperatures below the surface of the tropical Pacific Ocean, which may in turn raise sea-surface temperatures further in the coming months," the bureau said.

Unlike the last few El Ninos, the eastern Pacific is particularly warm, much like the "canonical" events of 1982-83 and 1997-98, Lynette Bettio, a senior climatologist with the bureau said. Model projections also have the event lasting well into next autumn.

The Southern Oscillation Index, which measures the pressure difference between Darwin and Tahiti, had also dropped sharply in recent weeks, one gauge watched closely by farmers worried about the rainfall outlook, she said.

El Ninos are characterised by central and eastern parts of the Pacific warming relative to those in the west. One result is that the normally easterly trade winds slow or reverse, with rainfall patterns tending to shift eastwards away from eastern Australia and south-east Asia.

Cool patch coming

While global temperatures tend to be boosted by El Ninos, the pattern does not mean all regions are warmer than usual for the event's duration.

Australia, for instance, is about to enter a relatively cool patch mostly as a series of powerful cold fronts from the south penetrate unusually far to the north.

The first of them should move across south-eastern Australia on Friday and Saturday, and "is going to be the coldest front of the year", Tristan Meyers, a meteorologist at Weatherzone, said.  (See below for Sunday's synoptic chart.)

Temperatures will be noticeably cooler in Melbourne, with the maximum dropping from 15 degrees on Thursday to 11-13 from Saturday to Tuesday. In Sydney, relatively mild maximums of 19 degrees on Friday and Saturday will retreat to 15 degrees by Sunday.

"We're going to see some frost up in south-east Queensland," Mr Meyers said.

Towns such as Stanthorpe will likely have a top of just 8 degrees on Sunday and Monday, with overnight lows of minus-2 to zero, according to the bureau.

While the front as a while won't be bringing a lot of rain, the ski resorts should receive another 10 centimetres or so of snow to boost their thin natural cover, Mr Meyer said, adding that more fronts won't be far behind.

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