The focus in the land of climate drivers should now be shifting towards the Indian Ocean as we track a very strong signal for the IOD to turn negative. The question remains is it turning negative now as a follow through from the lack of cyclone activity through the Basin this wet season, leading to a warm base as we head into the cooler season? Does that give it the vigor to see a strong Indian Ocean Dipole event take shape?
I have been talking about this for some time now about the risk of a wet second half of Winter into Spring 2022. But there is some chance that this can be dragged forward as well and we could start to see significant rainfall chances emerging over southern and western Australia.
In the short term, we have some chance of a large cloud band forming with a deep trough and tropical incursion sweeping through WA and then moving southeast into the Bight and then the southeast states.
The importance of westerly winds and the behavior of the SAM is also crucial. We need to see it turn negative for the westerly wind belt to come into play. That will then allow the moisture to be drawn southeast and south through the nation.
So this outlook looks at the Indian Ocean and the relationship with the SAM and the importance of drivers being in phase with one another.
SHORT AND MEDIUM TERM INFLUENCE - THE IMPORTANCE OF THE SAM BEING IN PHASE TOO!
We may see something similar to below in terms of additional Autumnal rainfall.
Upper level wind pattern - Next 2 Weeks
This really shows you the pattern shifting between the positive SAM phase and the negative SAM phase with the upper level lows in place for the short term, being overrun by the westerly wind belt and broader moisture being drawn into the upper northwest winds and that is when the Indian Ocean impacts will be felt. Is it the IOD being in a negative phase? No, but it does highlight the impacts of when moisture is running high through the eastern basin that things begin to shake and bake.
Precipitable Water Anomalies - Next 2 Weeks
Certainly highlights the transition from the positive SAM phase to the negative SAM phase and you can see here, the positive SAM phase in the short term leading to the moisture being biased in the east. But the Indian Ocean can only really sing when we have a negative SAM phase in the cooler seasons as outlined by the moisture streaming in via the jet stream in the medium term. Regardless of whether this indeed verifies, it is a great tool for trying to understand the basics as I continue to rattle off weather information to you.
Simulated Satellite Imagery - Next 2 Weeks
Once again, highlighting the initial rainfall in the east over the weekend and into next week is via the positive SAM phase and the rainfall spreading nationwide in the medium term is the negative SAM phase opening the door for the jet stream to become more wavy, sending in large volumes of moisture across the country.
Surface Pressure Pattern - Next 2 Weeks
The surface pressure pattern pulling all the data together shows that rainfall and cloud mass extending in the short term out west and medium term through the nation via the Indian Ocean only becomes more of a feature as we transition into the negative SAM which takes place in early May.
LONGER TERM IMPACTS INTO WINTER
Indian Ocean Dipole Forecast - Curated Forecast - Mid April Spread.
No change in the latest update here. The forecast for the Indian Ocean Dipole is to turn sharply negative through the second half of Winter with the event likely to peak during Spring. The impacts of the IOD will be felt during Spring more than Winter, however, this does not mean inland areas will not see above average rainfall and temperatures through tropical and northwest Australia will not remain elevated as a result. But the weather will certainly tend wetter as we go through Winter from July onwards through SA and into the eastern states. Spring looks very wet at this time, but the confidence on specifics for one given point is so low. But the trends, and this is what this forecast is about, is showing a trend towards another negative IOD. Can it change? Sure can and we have seen that happen in a heartbeat. So be aware that forecasts can move around quickly in this region.
June to August 2022
No change to the guide. The Indian Ocean Dipole is forecast to shift warmer through June and more likely through July, when the impacts of the IOD is felt across the nation.
Above average temperatures over northern Australia with the chance of rainfall higher than normal (may be a poor dry season for the north.
Across the southern and eastern areas of the nation, we should see above average rainfall in most (not all) districts from southern WA through southern and eastern SA and into VIC and NSW (mainly over inland areas). This is likely to become more of a feature as we move into August.
August to October 2022
Current data sets coming through in the past few days have strengthened the signal for a negative IOD for the Spring 2022. This would lead to above average temperatures and humidity values over northern Australia. The early onset of wet season rainfall/build up very much likely after a disrupted dry season.
Above average rainfall and cooler than normal weather for large parts of southern, central and eastern inland portions of the nation would be unfolding during this period on the current guidance. Note that this forecast will tighten and will likely soften a little too. But these signals are stronger than last year.
International Model Spread - IOD - Tending Negative - June 2022
The BoM model last year went early with the negative phase developing through the Eastern Basin. I am leaning more with the Euro on this one.
International Model Spread - IOD - Tending Negative - July 2022
BoM too aggressive, leaning more with the Euro.
International Model Spread - IOD - Negative - August 2022
The IOD will likely increase in strength from August as per last year which is expected to then be reflected with higher rainfall rates for large parts of the nation and then indeed temperatures over northern Australia will be well above average (as I have been talking about since February when I was back in Darwin talking with the elders up there with their forecasts for the remainder of 2022/23.)
International Model Spread - IOD - Strong Negative - September 2022
I fully expect the IOD to bottom out lower than last year and this event could be more prolonged than last year too as we head into Spring 2022. This could lead to a moderate to major flood risk for areas of southeast and eastern Australia. This is something for the back of your mind and not in the front of your mind just yet, but something to track here every fortnight as we move through the cooler growing season.
SEA SURFACE TEMPERATURES
Euro Sea Surface Temperature Outlook - June through August 2022
Above average sea surface temperatures (something I have been talking about for months now) will clearly have major impacts on rainfall and humidity values throughout the nation. This will start to be observed more from July onwards I suspect.
Euro Sea Surface Temperature Outlook - July through September 2022
The warmer waters look to strengthen and expand near and to the south of Indonesia and extend throughout the classic region where we see extensive cloud bands and rainfall events emerge through the Winter across Australia. But, as per last year, we can have the warmer waters, we need other climate drivers to be in phase (negative SAM etc)
Euro Sea Surface Temperature Outlook - August through October 2022
The peak of the IOD is typically in September through October and the waters reflect that but note how the warmer waters extend way down the west coast of WA. This could send in very wet weather with onshore winds and frontal weather, away from cloud bands from the northwest, so this is an ominous look for a very wet period once again for western, southern and central/eastern inland parts of the nation.
Euro Rainfall Outlook - June through August 2022
Note the rainfall coverage is excessive for large parts of the nation but looking at the broader data sets, this looks to kick in from July and August I suspect, so the devil is in the detail. Wetter as we go seems to be a good forecast on current data.
Euro Sea Surface Temperature Outlook - July through September 2022
Note the rainfall becomes very much above average for large areas of the nation, with many centres forecast to reach 70-90% values above the norm for this period and I want you to focus on Indonesia and offshore northern Australia which supports the IOD in negative phase, higher rainfall anomalies there signals the phase is rather strong.
Euro Sea Surface Temperature Outlook - August to October 2022
Early onset rainfall, widespread rainfall extending from the northwest as well and widespread rainfall via cold fronts and inland troughs. This is a very wet look at would rival 2016 standards for inland areas. So that is an analogue to consider when looking at this event at this time. But it will likely chop and change.
IRI Rainfall Outlook- June through August 2022
Also supporting a very wet look across the nation with the Indonesian Archipelago looking very wet which supports the negative IOD through Winter, more likely from July onwards.
IRI Rainfall Outlook- July through September 2022
Note the rainfall signals are strengthening for inland areas of QLD, NSW and into VIC and decent rainfall chances for SA through this time. The northwest also seeing early onset rainfall opportunities this next wet season.
RAINFALL FORECAST - PRELIMINARY
The theme from this output forecast is wetter as we go through southern and eastern areas of the nation and I will certainly be refining this forecast over the coming weeks. But something to watch, especially for inland areas, where flooding could become a concern for central and eastern areas.
Euro Temperature Outlook- June through August 2022
Warmer than average conditions for large parts of the north reflects the above average SSTs through waters north of WA through the NT and into QLD. With the large amounts of moisture, this will lead to more cloudy skies and cooler than average temperatures are possible with the wetter signal for southern and central inland of the nation. Coastal areas would likely see seasonal conditions and warmer nights.
Euro Temperature Outlook- July through September 2022
The cooler signal through Winter and into early Spring indicates the negative IOD phase strengthening with the rainfall rates and frequency increasing as we track into August and September. So once again the higher impacts from the negative IOD phase will be found during the second half of Winter.
Euro Temperature Outlook- July through September 2022
Even stronger signals for classic temperature distribution through the nation. Warmer and more humid over the northern tropics with thick cloud cover for longer duration over central and southeast parts of the nation leading to widespread rainfall and cooler days. Nights will still be warmer generally (not devoid of frost).
IRI Temperature Outlook- June through August 2022
Noting the temperature anomalies running high over northern Australia with the higher moisture content thanks to the elevated SSTs throughout the region. Not seeing huge signals for colder weather developing over inland areas and that could be quite right, given the elevated SSTs across most waters surrounding Australia.
IRI Temperature Outlook- August to September 2022
Once again noting that the IOD phase strengthens through Winter and begins to peak through early Spring and you can see that reflected in the below average temperatures being forecast for this period. That is directly linked to larger rainfall spread.
TEMPERATURE OUTLOOK - PRELIMINARY
Temperatures will get cooler than normal as we go along, and the southwest could be in for a decent Winter this year with frequent cold fronts and cloud bands moving through the westerly wind belt. The eastern inland could be cooler with persistent cloud cover and above average rainfall that is being analysed by the modelling. Northern areas of the nation will be warmer and more humid this dry season with elevated SSTs. Nationally the days could be cooler than normal but with elevated moisture levels across the country, overnights may be warmer than normal, offsetting the frost risk and the snow season could be impacted by this too.
So that is the general data sources that make most sense and are easy to consume but I will have a broader update on this after ANZAC Day when the next lot of data comes in.