The likelihood of a La Nina weather pattern forming late this year has doubled, but the chances of associated high rainfall are small, according to the Bureau of Meteorology.

Models suggest the tropical Pacific Ocean will continue to cool, raising the chance of a La Nina to at least 50%.

The bureau says if a La Nina occurs this year it will likely “be short and weak”, due to predicted warm sea surface temperatures early next year. A weak La Nina could even result in heatwaves in southeast Australia.

“La Nina events typically bring above-average rainfall to eastern Australia during late spring and summer,” it says. “However, given the competing influence of other climate drivers – weak warm waters north of Australia and cooler waters in the eastern Indian Ocean – current climate outlooks do not favour widespread rainfall across Australia for November-January.”

Following a brief warm period, tropical Pacific Ocean surface waters have cooled significantly in the past two weeks.

Atmospheric indicators of the El Nino Southern Oscillation, including the Southern Oscillation Index, trade winds and cloudiness near the Date Line, are approaching La Nina levels.

Seven of eight international climate models predict sea surface temperatures will reach or exceed La Nina thresholds by next month, but indicators need to remain at La Nina levels for at least three months to be considered an event, which is forecast by six of eight models.