La Nina, the weather pattern responsible for Cyclone Yasi and the Brisbane floods, has developed again in the Pacific Ocean.

University of Southern Queensland climatologist Roger Stone tells ABC News Online what we should expect from La Nina this time around.

What is La Nina?

La Nina means there's cooler-than-normal water in the central and eastern Pacific, usually contrasting with very warm water in the western Pacific - around the Coral Sea and places like that.

It then has an impact all around the world, not just for us.

Not all the effects are that disastrous, but certainly last year was an absolute classic - what I call Climate 101. This year is slightly different.

Sorry, this audio has expired La Nina expected to return ( Simon Lauder )

The consensus around the world is the Pacific Ocean is now primed to go back to a La Nina pattern again. All the preconditions are there.

The United States government has just issued an advisory saying it has already developed. It's not a matter of predicting it; it's already back.

What sort of impact is it going to have?

At the moment, it's just only out there, and it's in a pretty weak condition.

It's a bit later in developing than this time last year; for a start, it's running a few months later than last year.

The Americans are saying it will be an intense system by our mid-summer - around January/February.

At the moment, our climate models are showing above-normal rain over spring and beyond that, the potential for at least above-average rain as we go through summer.

Could it be catastrophic?

We don't know that yet. A lot of folks are saying it's too early to say how it will manifest, and that's true.

At this stage, you could say it's not as intense as this time last year - nowhere near as intense as this time last year - but it's only early days in its development, and it could become quite an intense system as we get through to January, February.

It's early days. With the exception of the United States model, most are saying at this stage, it's a weaker form than last year.

Just watch this space very, very closely to see how it unfolds.

How does La Nina affect Australia?

It can have quite an effect across Australia but it depends on how it forms.

The area of prime impact is around Queensland and eastern New South Wales - that seems to be the bullseye of the impact. North Queensland especially so.

It's the reason Lake Eyre can fill, as it did this year.

If it's a major La Nina, as it was last year, then Brisbane usually gets a major impact.

The flooded Queensland town of Theodore on January 1, 2011. ( Jackie Jewell: User submitted )

Even if it's a weak La Nina, it can still cause a lot of rainfall and a lot of cool, cloudy days.

Some of the smaller systems will just give us a decent wet summer, but mind you, just an average summer in Queensland can still pack a mighty punch because the state has had so many years of drought effects.

People have forgotten what an average summer can do to us in terms of rainfall.

What effect does La Nina have on the rest of the world?

Things happening in the Pacific have a global impact. La Nina can have incredible effects around the world, like El Nino.

So some parts of the world have almost the same signs as us - north-east Brazil, southern Africa, Fiji, and so on.

Like us, there is excessive rain in Indonesia, India and Pakistan, and parts of southern Africa.

At the same time in eastern Africa - around Somalia, Kenya and Ethiopia - they get excessive drought and famine and so does the south-western United States.

So you can get major impacts, such as the forest fires in Texas, the crop devastation in Texas, the famine in Ethiopia and Somalia.

The effects of El Nino and La Nina tend to echo around the world through what's called teleconnections; it sets up a pattern in one part of the atmosphere which then affects another part of the atmosphere.