“It's come on quickly and all of our model guidance predicts it's going to continue to strengthen,” David Jones, manager of climate monitoring and prediction at the bureau, said by phone. “A significant or substantial event is likely.”

The effects have already been felt before the official declaration. Morgan Stanley said in December that weather in South America for much of the previous month had been typical of an El Nino, citing above-normal rain in Argentina and southern Brazil and dry conditions in northeast Brazil. Palm oil, cocoa, coffee and sugar are the crops most at risk, according to Goldman Sachs Group Inc. last year.

Indian Monsoon

The monsoon in India, the world's second-biggest producer of sugar and wheat, may be below normal for a second year as the event develops, according to Harsh Vardhan, the country's minister of science and technology and earth sciences. El Nino is causing dryness in the Philippines, Oil World, a Hamburg-based researcher, said this month.

“Sea surface temperatures in the tropical Pacific Ocean have exceeded El Nino thresholds for the past month,” the bureau said on its website. “Trade winds have remained consistently weaker-than-average since the start of the year, cloudiness at the Date Line has increased and the Southern Oscillation Index has remained negative for several months.”

While El Nino increases the risk of drought in Australia, it's not guaranteed, according to the bureau. Of the 26 events since 1900, 17 have resulted in widespread drought, it said.

Cropping Areas

Farmers in eastern Australia will be keeping an eye on the forecast with planting of winter crops including wheat, barley and canola under way. Wheat production in the world's fifth-biggest exporter is set to increase 3.3% this year to 24.4 million metric tons, the government said in March.

“I don't necessarily think it will sway people given how good the start's been in most cropping areas around Australia,” Graydon Chong, an analyst at Rabobank International, said from Sydney. “It will have people worried if we continue to see a strengthening El Nino towards the second half of the year.”

Australia had raised the possibility of an El Nino for most of 2014 before tempering forecasts as changes to the atmosphere failed to develop consistently. The Bureau of Meteorology revived its prediction in March as the Pacific warmed. Japan's weather agency said on Tuesday that the event is likely to persist through the Northern Hemisphere's autumn.

Palm oil futures climbed as much as 1.6% to the highest level in five weeks in Kuala Lumpur on concern dry weather spurred by El Nino would curb yields in Indonesia and Malaysia, which account for 86 percent of world supplies. Indonesian production dropped 7.1% and Malaysian output fell 5.5% at the time of the last strong El Nino in 1997-1998, U.S. Department of Agriculture data show.

The U.S. Climate Prediction Center said that a weak El Nino developed in February and there's a 70% chance the pattern will continue through the Northern Hemisphere summer.

“We look at about 10 climate models and they agree entirely,” said Jones from the Australian weather bureau. “We know that once an El Nino event's established, it's very likely to last through to the end of the year.”

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