The risk of heatwaves and bushfire weather in southern Australia has increased, with the Bureau of Meteorology issuing an El Nino alert.

It means there is about a 70% chance of an El Nino developing this year – about triple the normal likelihood. And Indian Ocean conditions may reinforce the impact: in the west, a positive Indian Ocean Dipole (IOD) may have started.

“When combined, these two events in spring increase the possibility of a dry and warm end to the year,” the bureau says.

The events can make weather conditions more extreme in the south, but reduce the risk of cyclone activity in the north.

The tropical Pacific Ocean has warmed in recent weeks due to weakening trade winds, and models suggest further warming.

Four of eight models predict El Nino thresholds will likely be exceeded in coming months, with another two falling just short.

The bureau has had an El Nino watch in place since the middle of the year.

A positive IOD occurs when there are warmer surface temperatures in the west than the east, leading to weather system path changes. It can have a significant impact on agriculture, because events generally coincide with the winter crop-growing season.

The bureau says models suggest positive IOD values are likely to continue through spring, before returning to neutral values late next month or December.