The Bureau of Meteorology says there is a 50% chance of a flood-inducing La Nina weather system forming this year due to recent cooling in the tropical Pacific – which is more than double the normal likelihood.

The warning comes just six months since the last La Nina ended.

“La Nina events increase the chances of above-average rainfall for northern and eastern Australia during spring and summer,” the Bureau says.

A negative Indian Ocean Dipole (IOD), which can also increase rainfall, has weakened but the Bureau says the pattern of sea surface temperatures in the Indian Ocean remains likely to influence Australian rainfall over the coming months.

“Models suggest this weak negative IOD pattern could persist at borderline levels through October before easing further.”

The last La Nina started in September last year and continued until March this year, when major flooding hit NSW and Queensland.