Climate models project the Pacific will soon be ''on the cusp'' of an El Nino event, with warmer ocean surface temperatures already contributing to record warm and increasingly dry conditions across south-eastern Australia, the weather bureau said.

Surface temperatures in the tropical Pacific are running at 0.5 to 1.5 degrees above normal, and the normal trade winds have dropped or reversed to become westerlies, said David Jones, head of climate monitoring at the bureau. Sub-surface temperatures are 2 to 5 degrees warmer than usual.

Rowers enjoy Melbourne's unseasonably warm weather. Credit:Jason South

''A lot of the precursory signatures of an El Nino event are already out there in the Pacific,'' Dr Jones said, adding that there was a 70 per cent or higher chance such an event would be declared.

El Ninos happen about every three to eight years and tend to result in higher global temperatures. For much of Australia and countries to the north, they typically bring droughts and more active bushfire seasons as rainfall shifts eastward.