THE drought-breaking La Nina weather pattern has finally kicked in, bringing flooding rains along the eastern coast and filling the tributaries that feed into the dying Murray-Darling river system.

Forecasters are predicting a wet summer and autumn but remain unwilling - at least officially - to call the end of the worst drought in living memory. And they warn it would still take rains of "biblical proportions" to fill the dams of cities and towns.

As Adelaide sweltered through a 37C day that sparked bushfires across the state, the eastern states continued to enjoy good rainfall. One-in-20-year storms bucketed parts of Sydney and Wollongong yesterday, with 70mm falling in an hour in several suburbs.

National Climate Centre head of climate analysis David Jones said the current event was a "classic La Nina", with warm, humid conditions and plenty of moisture in the atmosphere. The southern oscillation index - the standard indicator of pressure systems in the Pacific region - stands at plus 10, indicating a return to wetter conditions.

Across the eastern half of Australia, a La Nina event became better established as sea surface temperatures dropped in the eastern Pacific and waters off Java became warmer than normal.

The wettest conditions in a decade in western Queensland have put a spring in the step of locals and raised hopes that the Murray-Darling is in for a reprieve. The Bulloo Highway west of the township of Eulo has been cut for a week by the flooded Paroo River. "We moved out here from Brisbane three years and we haven't seen anything like this before," said 11-year-old Samuel Baker as he played in the flood waters with classmates.

"This is the best rain we've had in years," said Eulo General Store owner Gary Berghoefer.
"The Paroo has been three or four kilometres wide in places. The rain will allow restocking onproperties that have been hurting."

Murweh Shire Council chief executive Chris Blanch said Charleville had 160mm of rain over the past month.

"Years of dust is being washed off everything. Plants and trees are sprouting new growth all over the place. It's a godsend," Mr Blanch said.

Warm water promotes convection and stronger westerly trade winds brought by La Nina blow moisture towards Australia, promising a return to good rainfall.

The La Nina is expected to remain until about April.

But Dr Jones warned that long-term rainfall deficiencies - especially around Melbourne, the Murray-Darling, Adelaide and southwest Western Australia - meant a return to full dams was "difficult to imagine".

"Large reservoirs in the southeast have been drawn down over the last decade and at this stage it's difficult to imagine those returning to pre-drought conditions in any foreseeable time frame," Dr Jones said.

"Of the large catchments in the Murray-Darling Basin, most are around 20 per cent of capacity and they will be drawn down over summer.

"Unless we see rainfall of biblical proportions, these large dams will be close to empty come autumn." University of Southern Queensland professor of climate and water resources Roger Stone said it would take "more than one decent wet season to break the drought".

"Areas with major water shortages would need 200mm a month for a couple of months to make a serious impact on dam levels," Professor Stone said.

Murray-Darling Basin Commission director Wendy Craik said that while welcome, the Queensland rains would do little to boost flows in the Murray and Darling rivers. "What we really need is sustained rainfall over a much wider area," Dr Craik said.

Medium-term forecasts hold for cooler and wetter conditions for parts of the country.

In the week to next Wednesday, according to the US National Centres for Environmental Prediction, rainfall is expected to be 500 per cent higher than normal in the Hunter region of NSW, on the NSW northern tablelands, southeast and central Queensland, and central WA.

In the week to December 20, the NCEP forecasts falls of up to 150mm for northeastern NSW. Southeast Queensland and the southern half of Cape York peninsula can expect 85mm to 100mm, it says.

The NCEP says the southern half of Western Australia will be up to 2C cooler in the week to next Wednesday.

Dam levels have, however, changed little in the past week. Melbourne's dams held 39.7per cent of capacity, down from 40per cent last week.

Dr Jones said Melbourne's two-year rain total, this year and last, looked likely to be the lowest on record.

Brisbane's dams held 20per cent, Perth held 42.6per cent, Hobart's held 84.4per cent, and Canberra's 43.68per cent. Sydney's rose 0.7per cent to a four-year high of 59.5per cent yesterday. The main dam, Warragamba, was at its fullest since early 2003. NSW Water Utilities Minister Nathan Rees said there would be no easing of water restrictions, at least until dam holdings were at 70 per cent and there was a good outlook for more rain.

Yesterday, South Australia wilted in the heat before a relieving cool change swept in. At Ceduna, the temperature fell from 38C at noon to 22C at 2pm.