AUSTRALIAN farmers have been warned that a powerful drought-inducing El Nino is on its way.

Japanese forecasters believe the El Nino event will wipe out southeast Australian farmers' hopes of good winter and spring rain.

The forecast has come as a shock to farmers, as only last month the Japanese predicted the east Indian Ocean would warm, leading to more rain in southeast Australia.

But last week Japan's Frontier Research Center for Global Change released its June computer forecast showing Australia's drought would continue for the next six months.

"The strong El Nino has killed the negative Indian Ocean Dipole," JAMSTEC senior scientist Jing-Jai Luo said. "The problem is El Nino still has a strong influence on the Indian Ocean."

Farmer confidence in the Japanese model has grown in recent years, especially after JAMSTEC team leader Prof Toshio Yamagata reliably predicted the continuation of the drought in May 2007, months ahead of other climate analysts.

Swan Hill grain grower Geoff Nalder said farmers would pay a lot of attention to Prof Yamagata's forecast.

"He's been right on the money for the past three years," Mr Nalder said. "It's going to make us more cautious. We'll put our purchases on hold and trim back in other areas."

Victorian Farmers Federation grains group deputy president Andrew Weidemann said Prof Yamagata's latest forecast was depressing news for a lot of growers given the confidence many farmers had in the Japanese forecast.

"It sends a significant signal to change your management decisions given all the signs are pointing to a poor spring," Mr Weidemann said.

Ironically, Prof Yamagata said variation in the Indian Ocean sea levels suggested the evolution of a negative or rain-inducing Indian Ocean Dipole event.

But like his colleagues at JAMSTEC, Prof Yamagata said the El Nino would kill the IOD.

Australian Bureau of Meteorology oceanographer Oscar Alvers said El Nino events could push the IOD into dry or positive territory by driving strong easterly winds off the West Australian coast.

These winds pushed warm surface water towards Africa, causing an upwelling of cooler sub-surface water off the West Australian northwest coast.

Cooler water means less evaporation, reducing the likelihood of northwest cloud bands forming and reaching southeast Australia.

"When we see prolonged easterlies this time of year in the Indian Ocean they seem to trigger a (dry positive) IOD," Dr Alvers said.

"We often get a concentration of the IOD and positive IOD event."

But while the climate models are predicting a gloomy outlook, US satellite images of the east Indian Ocean show it is still warmer than average.

Climate analysts warned against assuming the development of an El Nino was guaranteed.

Dr Alvers said Pacific sea surface temperatures are showing the spread of warm sub-surface water towards South America, which is one of the strongest indicators of an El Nino.

But Dr Alvers said the atmospheric conditions were yet to shift into the El Nino mode.

Dr Jing-Jai cautioned there was always some uncertainty with the forecast, given the JAMSTEC team was running its old climate model on a new computer system.

"I always say there's some additional uncertainty in running it (the model) on a new computer," he said. "So please be careful."

The latest JAMSTEC forecast is sure to depress irrigators and poses major problems for government and communities reliant on the Murray Darling Basin.

The South Australian Government is due to announce whether it will go ahead with a temporary weir at Wellington to protect Adelaide's water supplies by the end of the month.

VFF water council chairman Richard Anderson said irrigators needed a decent allocation in the coming season to keep costs down in the face of poor milk prices.

"We hope they're (JAMSTEC) not right, but we can't ignore this," Mr Anderson said.

"I think people might source some additional feed and have a good think about how they use their carry-over (unused water from this season)."

Drought has already driven Dartmouth Dam down to 21 per cent, Lake Eildon 12.6 per cent and Waranga Basin to 15 per cent of their capacities.