Is this the beginning of the end?

Niña this, Niña that, from kids to adults, inland and coastal, the last two and a half years everyone's learnt the Spanish translation for little girl, and frankly, most are done with it.

At first, the rain was a great relief following the drought and devastating bush fires, but then it hasn't stopped for two years. Victorians and South Australians lamented with months on months of poor surf while East Coasters rejoiced. That was until the flood waters made offshore pumping 4-5ft surf on outer bars not quite as appealing.

The whole country has seen a transition in seasons right on cue with cold, polar air being advected up and across the country. Don't tell me you haven't been digging around to pull out your warmer wetsuits.

Just as the colder westerly winds start to dry out the sodden landscape, we've got the first real signs that the lingering La Niña signal may be coming to an end. I briefly touched on this in the last article, but a developing warm water Kelvin Wave has strengthened and started to spread east under the sub-surface of the Equatorial Pacific Ocean, and this looks to be the death-knell for a three-peat La Niña into next summer.

While we know that La Niña develops under stronger than normal trade-winds across the equatorial Pacific Ocean, piling up warm water to the west and upwelling cooler water to the east, what happens below the surface is the key to what's in store for the months ahead.

With the warmer than normal surface water piling up across the western Pacific Ocean, we see the eventual downwelling of this warm water signal, spreading down as far as 200-300m below the surface. This warm water signal starts to spread east, drawn in up the upwelling through the central and eastern Pacific, taking two to three months to arrive across the other side of the Pacific Ocean.

This is known as an equatorial Kelvin Wave. Explaining Kelvin waves would require another whole article, but suffice to say it's a sub-surface pulse of water - which can be warm or cold - that travels from west to east. They're important because they set off el Niño events and cease la Niña.

Warm, sub-surface Kelvin Wave starting to spread east

Cold phases promote upwelling and enhance La Niña events, providing a fresh source of colder, sub-surface water, while warm Kelvin Waves can kill off the positive feedback loop as the easterly trade-winds upwell the warmer water to the surface, resulting in a slackening of the easterly trade winds.

We saw a cold Kelvin wave moving through at the start of autumn, extending the current La Niña, but a warm Kelvin wave is now starting to slowly spread east under the Pacific Ocean, with it due to surface over the coming months.

This will warm the surface waters through the central and eastern Pacific Ocean, likely pulling us out of La Niña conditions. With it occurring during the period that La Niña's usually restrengthen for our coming summer, it looks to also kill off the chance for a three-peat La Niña.

The global models are now trending this way, but hold a weak Niña-like signal throughout our summer, but it shouldn't be anything like we've seen the past two years.

Niño 3.4 region Sea Surface Temperature anomaly forecast, showing a weakening of the La Niña signal into winter

It doesn't mean the end to wetter weather across the country through our winter and spring though, with the waters off Indonesia currently being warmer than normal, and due to warm even further. Known as a negative Indian Ocean Dipole event, this is feeding instability and moisture from the north-west of the country, south-east across inland Australia and will provide a wet signal that will extend into spring.

Meanwhile, the lingering effects of La Niña will continue to feed moisture into the north and north-east of the country.

So we've got a few more months of gumboot weather to come, however, the little girl is slowly heading towards the door.

The chance of above median rainfall for June to August. Source: BOM