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As we enter autumn La Nina is hanging by a thread.
The rain-inducing weather driver is waning by the day and will be gone within the fortnight.
In the Pacific Ocean La Nina is marked by cool waters and strong easterly winds, while it’s counterpart El Nino is marked by warm waters and weak winds.
Across the next two weeks easterly winds will come to a crawl across the Pacific Ocean.
This will help the waters to warm and will bring the middle of the ocean back to a near-normal state.
You can mark it in your diaries now. On March 14 the Bureau of Meteorology will declare the end of La Nina.
Autumn outlook
When you take a quick glance at the BOM’s seasonal outlook you’re sure to think much of Australia will be warmer and drier than usual this autumn.
This is mostly true, but the maps from the Bureau’s model may be a bit too strong.
Other forecast models are not quite as keen.
The best chances of seeing below-normal rainfall is in western and southern parts of Australia.
However, near-normal rainfall is favoured for the eastern tropics of Queensland and between Sydney and Hobart.
It’s worth remembering that in Sydney, autumn is the wettest season of the year.
So just because we are likely to shift from above normal rainfall to near average with the end of La Nina, don’t pack away the umbrella yet.
Temperature-wise I agree with the Bureau’s outlook of generally warmer than usual days and near normal nights.
It will be a slow descent towards winter, especially for coastal regions where above normal days and nights are likely.
El Nino is looming
Farmers fear El Nino. It has been the primary culprit for most of our droughts.
El Nino’s influence spreads around the world adjusting weather patterns on all continents.
Forecasting La Nina and El Nino in the autumn is fraught with danger, but we are starting to see all our ducks in a row.
Forecast models are becoming more confident on the El Nino forecast, but they are notoriously unreliable at this time of year.
Historically though, there are some trends about El Nino.
Out of the nine double and triple la nina events since 1900, six have been immediately followed by El Nino.
Looking at all of the La Nina events since 1900, there have been six occasions before this where sea surface temperatures have returned to normal by the end of March. Only one of those occasions failed to turn into an El Nino event.
Essentially, we are on track and following the forecast models as expected.
The rest of 2023
So if El Nino is looking likely, what will that mean for Australia?
Generally, it means extra sunshine, fewer rain events and increased temperatures for much of Australia, especially from winter to summer.
But the key word there is generally. Not all El Ninos are the same, just like all La Ninas are not the same.
We’ve just had three of them in a row. Brisbane was flooded in one La Nina and drier than normal in the next.
Essentially, the risks are rising for hotter and drier than usual weather.
This raises the threat of fire, particularly in the grasslands and cropping regions that are quicker to dry out than the forests.
Flash droughts are also a growing threat. Exceptionally dry spells can cause vegetation stress.
Even a few months of barely any rainfall could start causing major problems in farming regions.
Australia therefore needs to prepare itself to switch from wet and mild to dry and hot.
