INDIAN OCEAN REVIEW - THE CHANCES OF THE NEGATIVE DIPOLE RETURNING FOR WINTER INTO SPRING 2022.

There have been rumblings as I have mentioned for a few weeks now that we could be staring down the chance of another negative Indian Ocean Dipole leading to widespread rainfall through Agricultural areas moving into the second half of Winter and into Spring 2022.


The climate modelling across most international agencies are in good agreement that a drier than normal Winter and Spring from this vantage point, remains very low. Seasonal conditions remains the most likely outcome, but in recent times, the updates are getting wetter as we go along and becoming more aggressive for widespread heavier rainfall across the southern, southeast and eastern inland of the country.


Now there is some caveats as I sift through this data that doesn't get spoken about as much as weather forecasters, we want to appear to be right at all times (that is not the case here, it is not possible). The confidence in forecasting this far out on a driver which has proven challenging the past few years (many areas planned for heavy winter rainfall that never came in the past 2 years) remains low and won't improve until about May.


But I think it is important enough to show you where things are going, I look at it so you don't have to, and I show you what is important and of value to you.


So lets look at the latest data sets as that is what we have at the moment and they offer some glimpse of where things are going. I will use a couple of the international agencies that do not get talked about very much but do carry a high reputation and skill score in this space.


JULY TO AUGUST - LEANING NEGATIVE.

Current model data and reviewing the information suggests that the IOD will likely remain neutral through much of Winter but will likely start turning negative through August, which is from this point I would anticipate the rainfall and temperature observations to be realised across parts of the country. It is also important to point out the forecast confidence is low but this is where the data current stands and the risk for now is leaning negative.

AUGUST TO SEPTEMBER - DEVELOPING NEGATIVE IOD INTO EARLY SPRING

The current guidance is strengthening the signal for a negative IOD in around 6 months. Now it is 6 months out, but for the purpose of shifting the focus from the ENSO through to the IOD which will be our driving force for Winter and Spring weather which is crucial to many, this is the current data sets. THIS WILL CHANGE. At this time, the data is suggesting a strengthening IOD will lift rainfall chances above average for large parts of the nation and elevate temperatures and humidity over northern Australia, increasing the chances of early onset northern season rainfall. The filling season in SWLD of WA would be quite productive and could be protracted into early Spring, depending on how the IOD evolves. These specifics will become clearer as we get into May but more likely to get better accuracy from June and July.

DATA SETS

Sea Surface Temperatures Last Month.

So where are we with regards to the SSTs through the Basin? We are warm, but not as warm as it can be at this time of year. The signal is for the Indian Ocean to remain at about 0.5C-1C below normal over the coming 4-8 weeks which is normal. If there is any late season cyclone mischief, then we may see the values cool further but at this time, on current guide, expect not too much influence in the traditional sense of the traditional Indian Ocean Dipole. The values are similar to this time last year and the year before and that suggests to me that we are sitting in a situation where we could be looking at another negative IOD (wetter) more than a positive IOD (drier) on the current guide.

A closer look shows that slight warmer bias out over the Indian Ocean, but it is sitting at about 1C below where it should be at this time of year. That is on the back of the Summer Season. But overall, the basin is fairly warm and may maintain this warmth through the Central and Southern part of the basin before spreading back towards Australia in Winter and through Spring.

So lets move along to the various parameters that give a sense of where conditions are heading and look at some of the data sets (I have looked at about 60 parameters over the past day or so) which illustrate what we may expect from July onwards.


THESE CHARTS ARE FROM JULY INTO SEPTEMBER.

Euro Seasonal Forecast - July through September - Sea Surface Temperature Anomalies Forecast.

Noting the shades of deep red over the oceans northern, northwest and through the southern parts of the nation. That in itself will lead to excessive moisture loads being propelled into the atmosphere and linked into the westerly wind belt through southern areas of the nation over Winter. But relating this back to the Indian Ocean Dipole, these values are maxing out the likelihood of a developing negative IOD through Winter and into Spring 2022. This is far more aggressive than last year's signals at this time of year for the record so it is with some merit that we now pay attention to these outlooks more regularly and shift the focus from the ENSO region to the IOD for the coming 6 months. This should raise the eyebrows of farmers throughout the nation. The last time I saw such strong robust signals relating to SST anomalies was back in 2016/17 and that lead to cold season flooding over inland areas of the nation.

The elevated SSTs are developing through the IOD region south of Indonesia and northwest of Australia and likely in the process of strengthening from August onwards in my opinion but it could be earlier than that if this is right.

Euro Seasonal Forecast - July through September - Deviation from seasonal surface level pressure.

Noting that the shades of blue over much of the nation which denotes the chance of a higher probability that the period is dominated by lower air pressure. Now in saying that, it does not mean it will rain everywhere every day, but this would lead to a higher chance of rainfall being above average, increased cloudiness and temperatures leaning below average over parts of the nation. The interesting feature which to me signals that this model is suggesting a negative phase of the IOD, is that the air pressure is below average back through much of the northern basin bordering Indonesia. That signals that we could see a robust phase of the IOD which could lead to a very expressive late Winter and early Spring rainfall pattern across the nation.

This is quite unusual across northern and northwest Australia and it is not very often you see the anomalies so much below average across large parts of the nation. So will watch these trends.

Euro Seasonal Forecast - July through September - Rainfall Anomalies.

Another signal that Euro is leaning towards the development of a negative IOD is found in this rainfall dataset. You can clearly see that the values over the nation are elevated but it is turning your attention to Indonesia. When you see values that elevated across northern and northwest parts of the nation, this suggests a negative IOD is place and would likely see moisture broadcast right through the nation via the upper level winds feeding into troughs and frontal weather that accompany winter. That means frequent rain bands and above average rainfall potential. At this stage, this forecast is not as aggressive as we saw back in 2016/17 when we had the last major cool season flood for VIC, NSW and parts of SA. But being this far out, the confidence in specifics are low but we need to use this as a base in future updates to see where the models are going.

The values over the nation represents the higher rainfall associated with a developing negative IOD. Remember that the peak of the IOD influence is not realised until about October through early November. So the influence here is quite significant.

Euro Seasonal Forecast - July through September - Temperature Anomalies

The temperature anomalies are also another hint that a negative IOD is developing, when you see elevated temperatures being forecast over Indonesia and northern Australia, that signifies a more humid dry season with a chance of rainfall developing throughout the period which is anomalous (see above). Conversely more cloud and rainfall across the nation leads to the chance of seasonal to below seasonal temperatures across the period. The Euro is not as aggressive as the other models for the period but does give credence to the idea that we are looking at another Winter and into early Spring where we may not be looking at baking temperatures if this is right, but as always we have to watch trends moving through the coming months

Note the temperatures are above average over much of northern Australia which is line with the IOD developing and strengthening through the second half of Winter. Note the warmer bias about coastal areas in the south. That may be related to the overnight temperatures not so much day time in my opinion.

Euro Seasonal Forecast - April through September - Tropical Cyclone Forecast - Next 6 months.

I thought this was an interesting product as it does show that late season cyclone activity running over those warmer waters through the Basin is possible during April and May and while we are talking more about July through September above, it is possible that we could see enhanced rainfall chances and higher humidity based off this influence moving through the back half of Autumn. IF we see late season cyclone activity, it could cause some of the SSTs to moderate in pockets of the IOD region so will be watching closely. Not an overwhelming enhanced risk but there are signals for tropical weather to remain a feature through May.

I will have a Winter 2022 Outlook tomorrow looking at the season as a whole. But just wanted to give you context this week around the period from April to June and then the exit out of Winter with this post which is July through September.


There will be two phases to watch out for, the decline of the ENSO influence in the coming 6 weeks and the increased influence during Winter of the IOD. Now in saying that the IOD is forecast to be negative is misleading this far out, but as you can see above, we could see one develop and IF one develops, we may need to prepare for more severe weather issues related to flooding more than any other element again for large parts of the nation.


So just when you think it was heading to a drought as some agencies were tipping back in February, it is looking more and more unlikely.


With the IOD, we will know more about that in about 4 weeks when I do the next update on this particular product. Lets see how the models settle. From May, I will be updating this once a fortnight through the cool season.


151 views0 comments