El Ninos, caused by interaction between abnormally warm or cool seas and the atmosphere, typically trigger drought in eastern Australia and Southeast Asia, and floods in western parts of North and South America.
The chance of an El Nino this year was estimated at between 30% and 50% around double normal expectations for this time of year, the bureau said in an update of its El Nino report (www.bom.gov.au). El Nino chances remain elevated, it said.
An El Nino is blamed for causing Australia's worst drought in a century in 2002, which decimated crops and livestock. The present outlook was complicated by differences between international computer predictions for the next eight months, the Australian weather bureau said on Wednesday.
Most models were predicting neutral conditions with temperatures somewhat warmer than average, while about one-third predicted an El Nino. A model run by the Australian Bureau of Meteorology was strongly in favour of an El Nino event developing during the southern autumn and winter, it said.
Latest observations of ocean temperatures, wind, cloud and atmospheric pressure were inconclusive, the bureau said. Subsurface warming had reached the coast of South America but there had been little response in surface temperatures in the eastern Pacific.
Slight cooling had occurred in the western to central tropical Pacific during the past fortnight.