Once every 6 weeks I like to look out 6 months to bring some guide as to where the Climate Modelling is taking us so lets have a look at the drivers that are in place.
For this update we will focus on the Indian Ocean and the ENSO region (Pacific). The SAM is very volatile and really a short term climate driver, sometimes you cannot forecast it more than a few days out at a time. That is more useful in the short and medium forecasting packages.
Wet signal to increase as we go through August, building further in September, peaking October and November before waning into December and January.
Temperatures are expected to remain seasonal for most areas, warmer for the next 2 months over northern Australia with an early build up, cooler over the eastern inland with rainfall and cloud cover becoming more frequent.
More active storm season for the eastern inland.
Higher risk of inland flooding for Ag areas of NSW, southern QLD, northern VIC and eastern SA through Spring into Summer.
Early build up expected over the north of the nation with above average rainfall to start the wet season.
Rainfall Outlook Seasonal Outlook - August to October 2021
Rainfall to become more widespread as we go through the second half of August as the pattern begins to flip and we lose the westerly wind belt. The warmer the nation gets, the more moisture it can hold. This leading to more widespread heavier rainfall events as we drift through September and October looks very wet. To wrap it simply, the Indian Ocean Dipole being in negative phase with elevated SSTs around the north and east of Australia will lead to more productive rainfall events as we go through the coming 3 months. The tap will be turned on, but it may be a case for some areas, going from nothing to a full blast and not being turned off for a while. So that increases the risk of flooding for inland areas of NSW,/ACT, QLD, SA, VIC and TAS.
Temperature Outlook Seasonal - August to October 2021
Temperatures are set to be warmer than normal through the coming few weeks in line with the frontal weather bringing down the warmer northwest winds. But the heat engine should begin to see increasing clouds, that is inland areas of WA starting to pick up on more cloudy weather, dampening down the high temperatures as we go through the build up. This will lead to an average season over most of southern Australia. IF the higher than average rainfall frequency and distribution occurs through the outlook period below, then temperatures will be below average over large parts of inland SA, NSW and parts of southern QLD and northern VIC. That does remain a high risk on current guidance. The temperatures over northern tropical areas are likely to be warmer than normal, but connected to the higher humidity values and not being 5-7C above normal like you would experience in an El Nino. The build up conditions starting early.
Rainfall Outlook Seasonal- November 2021 to January 2022
The wet signal continues through November and December with the high levels of moisture from an early build up filtering south and east into the troughs over inland QLD, NSW and VIC. Storm season may be well above normal for many locations with severe weather season active overall for October through early summer. With many areas of inland NSW and VIC on repeated flood watch with light to moderate rainfall events, there is an elevated risk of flooding this spring throughout the eastern inland and this may extend into QLD through early summer if rainfall forecasts verify. Nothing is ever locked in weather wise but the signals from the climate drivers, climate models and global weather agencies are wet through to January.
Temperatures Outlook Seasonal - November 2021 to January 2022
With the increasing cloud cover and more rainfall over the north and east of the nation, the temperatures may be moderated for many locations with again a chance of below average temperatures over the eastern inland of the nation for the first half of summer. The season over all looks to be seasonal, yes there will be heat about, but this likely to be moderate by more regular rainfall. With the higher rainfall likely to be around the nation during the coming 6 months, producers should be aware of the potential for fungal issues, brown rot and other diseases that can arise in prolonged wet and humid periods. So even if you get a normal amount of rainfall, there is a chance you could have well above humidity values. So this is multipronged. This is a guided 6 month outlook and the forecast will likely become more refined in the coming months.
THE RISK OF FLOODING
This chart was prepared last week and will be updated again during early August. The risk over the outback connected to heavier rainfall through the inland QLD and NT. The risk of flooding not indicated over northern Australia yet, but this will be updated once I prepare the forecasts for the tropical outlook next week.
The overall forecast here is NEUTRAL. I am favouring a cool neutral for the Spring and Summer, however there are climate modelling that suggests a weak La Nina. In any case whether it is classified as a weak La Nina/cool neutral across the global weather agencies, the impact is the same. It will lead to a good chance of average rainfall and average temperatures for eastern and northern Australia.
THE RISK OF LA NINA DEVELOPING IS 60%.
The data sets are still mixed but the most reputable global agency shows that we have a weak La Nina that is possibly developing this spring. But just because this model suggests it and NOAA declares a La Nina watch does not make a La Nina event. But one thing we can take from this outlook is that we have no dry signal and no brutally hot summer on the cards AT THIS TIME. So that is some good news as many recover from the shocking drought and fires.
CPC/IRI Official Probabilistic ENSO Forecasts - Members spread.
You can see the seasonal shift from the current neutral and then tending towards a La Nina by October and that peaking through January before waning during Autumn, if this was to verify. There is a very very low risk of El Niño developing and a moderate chance of the neutral phase persisting, and I am leaning towards that forecast for now and will adjust my forecasts when the next data sets come out mid August.
The members in black show a modes bias towards the La Nina through the spring and summer, but note the members in the red, very low chance of an El Nino for the coming year. BUT an El Nino may return at the end of 2022 into 2023. So we must may the most of the rainfall while we have it. Traditionally, there is an El Nino that follows a potential double dip La Nina.
The BoM Outlook suggesting a cooler neutral for the ENSO region however a good portion of the global agencies are cooler than this and the BoM model has had a La Nina forecast in previous updates so watch this space.
The global model agencies for October show the split across the world in what will happen in the Pacific come October, again a slight lean towards a La Nina developing is fair but I will keep my forecasts cool neutral.
The climate mode rainfall anomalies
CANSIPS continues to support the other climate models above in the month to month run with the rainfall building through the Spring, peaking later November and then easing through December and into January (I wouldn't be too concerned about the red shading over the NT as that can be a signal the monsoon could peak in later December and then return to bring a bumper February of rainfall leaving January drier.) The signal for above average rainfall continues to be driven by the Indian Ocean primarily, with the lag effect persisting into January. This model DOES NOT factor in a La Nina.
Rainfall Anomalies October 2021
Rainfall Anomalies November 2021
Rainfall Anomalies December 2021
Rainfall Anomalies January 2022
Speaking of the Indian Ocean
There is little change in the guidance for the Indian Ocean over the coming 4-6 months with event still building and the likelihood of rainfall increasing as we go though August and more pronounced as the temperatures warm up over the nation. Higher temperatures means higher levels of moisture in the air and the ability for more rainfall to develop with lower air pressure.
The BoM forecast for the coming 6 months supports the wetter signal for the east and south of the nation and the chances of an early build up over northern Australia. The weather nationally expected to be largely connected to this driver for the coming 4-5 months before it wanes in January with the seasonal shift to summer and the monsoon.
The negative IOD is expected peak in October and November with the event likely to wane in the December. The BoM model is the most aggressive and early with the event which I do not side with as if we were as deep as the model is suggesting through August, we would be seeing more impact from the northwest to southeast, and I have not been satisfied that the model has got that right, so I am leaning with the Euro outcome at this time.
The Indian Ocean influence does become negligible over the summer months into early Autumn which is normal.
Indian Ocean Impacts Seasonally.
But where the moisture is coming from is important.
The further up the west coast of WA the moisture is streaming in from, the better the outcome, personally I like to see the moisture shift from coming in from south of Java and then into the Kimberly and northern Pilbara and then diving south or southeast into the frontal weather and inland troughs, so that is what we will be watching.
Keep watching the short and medium term forecasts over the coming few weeks, we are looking at that pattern flip in the second week of August which I do believe will start to shape the shift towards the wetter phase over inland areas. And that is being reflected in the medium term forecasts.
Euro 12z M - Rainfall for the coming 6 weeks
The signals of inland rainfall developing are increasing in the latest data set from the Euro this morning and I will have more on this later this week.