A La Nina weather system has not yet formed, but the Bureau of Meteorology warns that above average rainfall and flooding could still occur this spring and summer.

There’s a 70% chance of the system developing, but atmospheric and oceanic observations have yet to consistently reach La Nina levels.

“Regardless of whether La Nina thresholds are met, a La Nina-like pattern in the Pacific may still increase the chances of above-average rainfall for northern and eastern Australia at times during spring and summer,” the bureau said in its latest update today.

Several other weather systems are combining to point to wetter conditions across much of the country.

The negative Indian Ocean Dipole (IOD) has weakened, but cloud patterns in the eastern Indian Ocean suggest the atmosphere is still responding to warmer than average ocean temperatures in the region.

A negative IOD increases the chances of above-average spring rainfall for much of southern and eastern Australia.

Meanwhile, a Madden–Julian Oscillation (MJO) is forecast by some climate models to strengthen and move eastwards into the western Pacific over the coming fortnight. If the MJO strengthens this would increase chances of above average rainfall across north-east Australia, the bureau says.

The Southern Annular Mode (SAM) has been positive for the past three weeks, and is forecast to remain at positive levels to the end of the year.

A positive SAM during summer typically brings wetter weather to eastern parts of Australia, but drier than average conditions for western Tasmania.

The bureau is predicting heavy rainfall across much of the country this week.

“It will be an exceptionally wet and stormy week ahead for many parts of the country, with millions of people in the east and south-east to be impacted by some of the wettest conditions so far this severe weather season,” it said.