The chance of an El Nino this year was estimated at between 30 percent and 50 percent -- 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.

In Geneva, the World Meteorological Organisation (WMO) said that experts were divided on whether an El Nino was on the way, despite unusually warm sea surface temperatures.

"For the next several months, continuation of the currently neutral conditions or the development of basin-wide El Nino conditions are considered about equally likely outcomes," the UN agency said in a statement.

Further warming of sea surface temperatures in the eastern equatorial Pacific region were expected, and rapid changes were possible at this time of year, it added.

"The surface waters of the central Pacific have now been warmer than average since 2001. Such a prolonged period of warmth is highly unusual," the agency said.

CLIMATE PATTERNS

Already, unusual climate patterns observed in the western equatorial Pacific region in late 2004 and early 2005 were typical of El Nino and were likely caused by the unusual ocean temperatures, the WMO said.

These climate patterns included drier than normal conditions across parts of Malaysia, Indonesia, the Philippines and Southeast Asia, and the above-normal rainfall in late 2004 across parts of East Africa and the western Indian Ocean.

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.

Sub-surface 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.

Moderate to strong westerly winds had reached the western Pacific and were expected to produce more sub-surface warming, which would be very important in the development of an El Nino across the Pacific basin, the bureau said.