The chances of a flood-inducing La Nina weather system forming this year have risen, just six months after the last such event came to an end.

The Bureau of Meteorology says recent cooling in the tropical Pacific Ocean means there is a 50% chance of a La Nina forming, which is about double the normal likelihood.

“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.