By Michael Perry
SYDNEY (Reuters) - A key measure of El Nino weather patterns eased in June, suggesting the potentially damaging condition was not yet a certainty, although India's monsoon is likely to remain weak, Australia's weather bureau said.
An El Nino, which means "little boy" in Spanish, is driven by an abnormal warming of the eastern Pacific Ocean, and creates havoc in weather patterns across the Asia-Pacific region.
The Southern Oscillation Index (SOI), a key factor in identifying an El Nino that is calculated from monthly and seasonal changes in air pressure between Tahiti and Darwin, eased in June to negative 2 from negative 5 in May, the bureau said on Tuesday.
A sustained negative SOI often indicates an El Nino, which can bring drought conditions to Australia's farmlands, weaken the Asian monsoon critical for Indian crops, stir up storms in the Gulf of Mexico and cause flooding in Latin America.
"Minus 10 is an often used threshold level and it just got to there a few times, but it hasn't been sustained at that level," Sam Cleland, author of the Bureau of Meterology's weekly Tropical Climate Note, said on Tuesday.
"I don't think we'd make the call just yet that we have an El Nino event in place," he said ahead of the bureau's El Nino update on Wednesday.
For a graphic showing the SOI and El Nino since 1990 click:
http://graphics.thomsonreuters.com/079/AU_STHOS0709.jpg
The bureau's last report on July 2 said an El Nino was very likely in 2009 and may be declared in coming weeks.
The bureau -- one of the world's foremost Pacific Ocean weather watchers -- is not expected to formally declare on Wednesday the first El Nino since 2006.
"The equatorial Pacific Ocean continues to develop into a more El Nino-like pattern," said Cleland, manager of climate services at the bureau's Darwin office.
But the Pacific trade winds, another key El Nino factor, had also weakened in June, Cleland said.
"To call an El Nino or not is difficult and it takes a number of parameters over a sustained period. The formal definition of an El Nino often occurs in hindsight," he said.
The last severe El Nino in 1998 killed more than 2,000 people and caused billions of dollars in damages to crops, infrastructure and mines in Australia and Asia. It came in the middle of the Asian crisis that roiled financial markets.
India, one of the world's biggest producers and consumers of everything from sugar to soybeans, is already experiencing a weaker annual monsoon. Its faltering sugar crop has helped drive world prices of the commodity to their highest in three years.
India's monsoon will remain weak according to the latest Madden-Julian Oscillation (MJO) index, which gauges the eastward progress of tropical rain, Cleland said. It was too early to get a read on the potential intensity of a new El Nino, he added.
"There's no strong indication at this stage of what the level of impact this ENSO event could have," he said, adding that some weak El Ninos have had severe impacts on Australia rainfall, while stronger El Ninos have only had marginal impacts.
(Editing by Clarence Fernandez)
