The talk of any La Nina at this time is rather premature and I think it is important that before you read on, that any forecast that is swinging one way or the other for the end of the year for the ENSO is if low confidence and should be viewed in such light as data sets continue to evolve.
Current Guidance - May Outlook
The forecast is largely unchanged from earlier in April with the La Nina slowly dissolving over the Pacific, this retarding the recovery towards neutral conditions and lessening the impacts of further positive SAM events. This means we will see lessening rainfall impacts on the east during June through Winter. The waning La Nina also supports the emergence of more negative SAM events. This helps to invigorate the southern wet season between May and October. There is sufficient evidence that a La Nina emerges through December but for now I am forecasting leaning La Nina as I am not confident in the data this far out, but it certainly warrants some careful consideration over the coming updates.
So we are we sitting on current April data sets? The idea is that we are looking at the ENSO shifting into a La Nina, leaning towards another event unfolding. However, calling it this far out is not the purpose of this update, it is sharing with you where the signals are taking us and to certainly check back at regular intervals to see where it goes from Winter onwards.
A La Nina would be leading to heavier rainfall for the north earlier on in the season. The La Nina would also support a more active storm season from October and once again would lead to more Summer flooding for QLD and NSW, especially from February 2023 onwards.
But that is based off broad data and observations and it should be said that not one event is the same across the nation and with a waning negative Indian Ocean Dipole through the Spring into early Summer, we could be very wet over large areas of the nation meaning that many regions are primed for Summer flooding ahead of any expected La Nina forming.
THE FLOOD RISKS BEFORE ANY LA NINA IS MY CONCERN RIGHT NOW
The impacts on the nation if we do indeed have that waning Indian Ocean Dipole and the developing La Nina is formidable. That would result in very much above average rainfall over large areas of the nation from October through the warmer season and the flood risks peaking through the east coast once again between January and March 2023. So that is something to consider.
Flooding risks related to the eastern inland would be in response to the negative Indian Ocean Dipole between August and November and separate information on this will be available this week.
Winter Flood Risk 2022
You can see the impacts of the Indian Ocean Dipole on the rainfall distribution through the Winter Outlooks. That will lead to the higher rainfall being over on and west of the divide, and setting up an increased risk of flooding through the Spring of 2022.
Spring Flood Risk 2022
The flood risk continues to be excessive related to the Indian Ocean Dipole peaking but once again it sets up an elevated risk of flooding through Summer 2022/23 with any developing La Nina from November onwards. The risk sits at 65% at this time. So all this rainfall is in ADVANCE of any La Nina influence.
LA NINA AT A GLANCE - WHERE WE ARE PRESENTLY.
The impacts of La Nina have been clear over the past Summer and Autumn with the warmer waters right around the nation. The elevated SSTs lead to higher moisture content over Spring and Summer and this leads to more rainfall developing as moisture is drawn into troughs and low pressure. There is also a higher chance of low pressure sitting over Australia.
Current observations through to early April shows that there was some warming of the waters in the sub surface west of South America but it is not deep and there is more cooler water through the ENSO region through to about 250m which is significant at this time. This needs to be neutralised in the coming months if we are to avoid another La Nina event so this will be an area of interest over the coming months.
WHERE THE MODELS ARE GOING
The next update is due in 2 weeks but for now there is not much shift in the guide with the cool neutral to persist over the ENSO region of the Pacific and with all that cooler water circulating at depth, it will be very hard for the basin to recover to past cool neutral at best for the remainder of the year. More international agencies are supporting a weak La Nina at this time, with only one agency suggesting an El Nino.
The Rainfall Outlook for Spring 2022
This is all connected to the Indian Ocean Dipole. But the concerning factor in this, it sets up the threat of a severe flooding if we do see a La Nina developing. I have not seen such a wet signal off the modelling sine I have been following this particular data in the past decade.
The Temperature Outlook for Spring 2022
Warmer weather over northern parts of the nation is in direct line to the Indian Ocean Dipole and not in response to the ENSO, but if we do see a La Nina building through the Spring into Summer, the humidity, temperatures will reflect what we have seen in the past year but at a more enhanced level.
So I will leave this here. But for now the threepeat remains to be seen and here is the possibility of where things could go in our third cycle.
More this afternoon in your state based forecasts.