The Bureau of Meteorology is on alert for yet another La Niña season.
There's a 70 per cent chance that Australia's east coast will have to contend with the climate driver for a third year in a row.
This is very unusual, and other countries have already declared La Niña. Let's get up to speed with what it might mean for this spring and summer.
1. What is a La Niña?
La Niña is one of the main climate drivers for eastern Australia. It brings with it a greater chance of rainfall.
Basically, it's a phenomenon determined by changes to winds and water temperatures in the tropical waters of the Pacific Ocean.
Along with the complementary El Niño, the phenomenon is referred to as the El Niño Southern Oscillation or ENSO.
So, for Australia, El Niño typically leads to drier and hotter conditions, while La Niña usually leads to cooler and wetter conditions.
You can read up on the latest update here: Australia remains at La Niña alert amid near-record Indian Ocean Dipole event
2. Why should we care about it?
La Niña brings with it an increased chance of above-average rainfall, and the east coast has already endured two La Niña seasons in the past two years.
Flooding devastated communities across the eastern states just months ago.
Now we could be facing a third straight season. This has previously only happened three times since 1900, according to the bureau.
And two of those triple-dip years coincided with major flooding events.
For more on previous triple La Niña seasons check this out: Australia's east coast set for third straight La Niña season, experts predict
3. What actually causes a La Niña?
Basically, the process is kicked off by trade winds. These are the winds that blow east to west around the equator.
When these winds blow stronger, they can change ocean currents.
This eventually leads to warmer water surface temperatures in the western Pacific to the north of Australia.
The warm water means conditions become more favourable to rainfall because of more moisture in the atmosphere.
When certain thresholds are met, weather authorities declare a La Niña.
So, La Niña doesn't directly cause rainfall, it just primes conditions for it.
Find more detail here: What is the La Niña and what does it mean for Australian weather?
4. Why have other countries declared a La Niña but Australia hasn't?
Agencies in the United States, the United Kingdom, Japan and India say the La Niña has been underway for a little while now.
The Bureau of Meteorology (BOM) doesn't because it has a more rigorous process for declaring a La Niña. Climate change is also making things more difficult, which you can read more about here.
That doesn't mean the BOM won't declare a La Niña this year. The next climate driver update from the bureau is in about two weeks, on September 13.
In a climate outlook last week, the bureau said: "the September to November rainfall is likely to be above median for most of the eastern half of Australia, but below median for western Tasmania and south-west Western Australia."
Look back at the forecast: BOM's latest outlook signals soggy spring weather for eastern Australia
5. Is it just La Niña that could cause higher rainfall?
No, there are other factors at play. Another big driver is the Indian Ocean Dipole.
A Negative Indian Ocean Dipole event brings more rain to Australia. It's defined by differences in temperatures in the east and west of the Indian Ocean.
During a negative event, which we're currently experiencing, winds become more westerly which eventually brings more rainfall in the Top End and southern Australia.
Check out more here: What is a 'negative Indian Ocean Dipole' and why does it mean more rain for Australia's east?
