Forecasters in Australia and New Zealand warned yesterday of the possible onset of an El Nino, reviving concern the weather pattern that can bring drought to parts of Asia may return for the first time since 2010. Tropical Pacific temperatures have exceeded El Nino levels for a month and the Southern Oscillation Index, or SOI, has remained at or near thresholds for three months, Australia's Bureau of Meteorology said in a statement. Patterns are consistent with a weak event developing, New Zealand's National Institute of Water & Atmospheric Research said separately. El Ninos, caused by periodic warmings of the Pacific, can roil agricultural markets worldwide as farmers contend with drought across parts of Asia or too much rain in South America. Forecasters, including scientists from Australia, raised the possibility of an El Nino developing earlier this year, before tempering their outlook as conditions for the event didn't develop. "Further warming of the tropical Pacific Ocean is likely, so it also remains possible that the ocean and atmosphere will fully couple in the coming weeks to months," Australia's bureau said in the fortnightly update. "If an El Nino is established, models suggest it will be weak, or moderate at best." While some indicators are close to or exceed thresholds, others have remained near-average or only temporarily approached El Nino levels, Australia's bureau said. That indicates the interaction between the ocean and atmosphere required for an El Nino to be declared may not be fully locked in, it said. El Ninos, caused by periodic warmings of the tropical Pacific, occur every two to seven years and are associated with warmer-than-average years. The last El Nino was from 2009 to 2010.