Shifting sea surface temperatures in the central Pacific have put Australia back on "La Nina watch", raising the prospect of a return to flood conditions.

The Bureau of Meteorology says there are early signs that an event may form in the Pacific Ocean later this year. 

“When La Nina watch criteria have been met in the past, a La Nina event has subsequently developed around 50% of the time,” the bureau said last week.

There is about an equal chance of neutral conditions prevailing during the outlook period. 

La Nina events are normally associated with above average winter, spring and early summer rainfall over much of Australia, and an increased risk of flooding.

Australia recently emerged from an El Nino, with neutral conditions now prevailing. El Nino is more associated with dry weather and conditions favouring bushfires.

The bureau says sea surface temperatures in the central Pacific have been steadily cooling since December. This is supported by a significant amount of sub-surface cooling in the central and eastern Pacific. 

Bureau climate manager Karl Braganza says rainfall and temperature forecasts are not based on the status of the El Nino-Southern Oscillation Outlook and the best guidance for future rainfall or temperature is the long-range forecast. 

“The long-range forecast for June to August is showing an increased chance of above average rainfall for parts of eastern Australia, and parts of WA and SA,” he said.  
 
“There are roughly equal chances of above or below median rainfall for most of eastern Australia, including much of Queensland, NSW, Victoria and Tasmania.”