INDIAN OCEAN INFLUENCE - WHERE HAS IT GONE? IS THAT IT FOR THE NEGATIVE DIPOLE?

NO! No, it is not and before you start throwing in the towel at the weather, pay attention to what is happening in reality. Look at the influence in real time and this post is looking at the observed data and the forecast data and where we are going at the moment. We have to work with what we have got, not with what we WISH we had! So, let's see where we stand.


I alluded to this yesterday in the broader ocean update, that we are surrounded by warmer than normal waters at the moment, in regions that supply a large amount of influence on rainfall being recorded at above average levels.


So, while it is quieter now, lets compare where we are this year to last year.


INDIAN OCEAN FORECAST 2021

Indian Ocean Dipole Forecast for the remainder of 2021 - BoM/POAMA model. Valid June 8th 2021.

SEA SURFACE TEMPERATURES JUNE 2021

The temperatures through the Indian Ocean were somewhat normal,with only a slight warming over the Indian Ocean and also note the ENSO region too, with a full recovery to neutral conditions there. This is why the rainfall failed last year in the Winter for most of Southern Australia. Understand that the forecasts through Winter are of low confidence.

OUTCOME OF THE INDIAN OCEAN DIPOLE LAST YEAR

Many areas struggled to see rainfall from the Indian Ocean Dipole event due to the persistent ridging and dry air over northwest and western Australia, which followed a wet Autumn. We are seeing that play out again this year so far. But the big difference is that during June into July, the temperatures actually cooled through the Basin which led to the event being very limited through Winter and it was only into Spring we saw the negative event crank into gear, this bringing rainfall into the southeast and eastern states well into Spring and early Summer. The lack of rainfall caused grief for farmers in SA and VIC where crops struggled to get up and going.


INDIAN OCEAN FORECAST 2022

Indian Ocean Dipole Forecast for the remainder of 2022 - BoM/POAMA model. Valid June 15th 2022.

The current rate of warming through the Indian Ocean is steady with a general 1.5C degree anomaly above the average through the region that brings us widespread rainfall through late Winter into Spring where the event peaks, so looking at the temperature gradient through the Indian Ocean, we are starting to see the classic signs that a negative phase is developing. This is a key difference to this time last year. I suspect we will be seeing an elevated period of influence from the Indian Ocean from August through to December as advertised here since January. The influence peaks during the Spring and anything before hand is a "bonus" for areas of southern and southeastern parts of the country. Another area that we are seeing of influence is the warmer waters north of Australia which we are seeing in full force this week.

SEA SURFACE TEMPERATURES JUNE 2022

It is a very different year across the waters surrounding Australia, hence why rainfall forecasts are off the charts. But it comes down to the synoptic pattern and if we end up with blocking patterns across the nation. We are seeing one right now, and that is tapping into very deep moisture around the nation and this is being lifted into rainfall. Note that the Indian Ocean is one of the ports that will influence rainfall being above the average as we move through the remainder of Winter but for southern Australia, understand, that the rainfall intensity won't match what is happening over the northern and eastern parts of the country until we get into Spring. Northern and Eastern Australia, we should see further rainfall across the course of dry season with the early onset rainfall to increase further from August thanks to the Indian Ocean strengthening and combining with the warmer waters north of the nation.

So, what are the impacts moving forward and when can we start to see that rainfall coming back?


GFS 12Z - Precipitable Water Anomalies - Next 2 Weeks

You can see the impacts of the high pressure over northern WA and the drier surges sweeping through the southeast to easterly flow, which is dominant over the coming week or two, that drier air, spreading through the lower levels right through south of Indonesia, limiting rainfall and convection through the region. But it will be with the shift to the westerly wind regime into the second week of July, that we start to see moisture drawn south and southeast via upper-level winds into the westerly waves bringing up the chances of rainfall along the cold fronts and possibly some cloud bands across the country, but with ridging nearby, the rainfall may be limited for another 2 weeks across the nation. Noting that moisture values do increase heavily south of Indonesia through the medium term but has little impact on Australia through this period until the 15th of July.

GFS 12Z - Upper-Level Winds at 18000ft where the pressure is 500mb - Next 2 Weeks

The upper-level winds are generally light through the Indian Ocean with the main wave action further south at the moment, thanks to the Southern Annular Mode being in a positive phase leading to a suppression of the impact across WA. With an upper high and ridge parked over WA this is helping to push the moisture back towards the Central Indian Ocean and drier air is stuck over the traditional IOD zone bringing the rainfall chances up for WA and through the country. But this is not unreasonable at this time of year, and ridging should be in place across this region for the coming 2-4 weeks at least before we see some chance of low pressure forming near Indonesia. The upper level winds will back into the northwest once the frontal weather returns to the south of the Indian Ocean, this helping to propel the moisture into the nation. But that does not look to occur until we get to the second week of July.

GFS 12Z - Simulated Satellite Imagery - Next 2 Weeks

As you can see there is little northwest cloud band activity with the frontal weather also well to the south for the coming week before it returns to the southern parts of the nation from about the end of the first week of July. The pattern is not in phase with the higher SSTs yet and with the absence of cloud cover and clearer skies, this may assist in the warming process of the waters through the northern Indian Ocean. So while it is quiet for the coming 2 weeks, that may not be the case through the remainder of July and into August.

RAINFALL IMPACTS IN THE LONGER TERM FROM THE INDIAN OCEAN.


INDIAN OCEAN TO INCREASE INFLUENCE THROUGH JULY, MORE SO THROUGH AUGUST AND INTO SEPTEMBER IN COMBINATION WITH THE WARMER WATERS OVER NORTHERN AUSTRAILIA.

SPRING RAINFALL TO BE EXCESSIVE BASED OFF THE CURRENT SIGNAL OF THE INDIAN OCEAN DIPOLE PEAKING AND THIS IN COMBINATION WITH THE WARMER WATERS OVER NORTHERN AUSTRALIA.

TEMPERATURE IMPACT FROM THE INDIAN OCEAN DIPOLE AND WARMER WATERS NORTH OF AUSTRALIA.


WINTER TEMPERATURES REFLECTIVE OF THE INDIAN OCEAN DIPOLE WITH THE WARMER WEATHER IN THE COMING 6 WEEKS OVER MUCH OF THE NATION BECOMING COLDER OVER THE INTERIOR AS CLOUD AND RAINFALL INCREASES. WARMER AND MORE HUMID OVER THE NORTH IN JULY AND AUGUST.

WITH EXCESSIVE RAINFALL, SPRINGTIME LOOKS COOLER THAN NORMAL FOR LARGER CHUNKS OF THE COUNTRY WITH THE WARMER BIAS OVER THE NORTH STARTING TO EASE AS EARLY ONSET RAINFALL GETS UNDERWAY THERE TOO.

So while it is frustrating for farmers in the south and west, the Indian Ocean influence will continue to increase over the course of Winter and peak in the Spring. Rainfall rates may be somewhat more seasonal along the west coast of WA with the bulk of the warmer waters influence bypassing the SWLD at this time, via the strong upper level northwest winds.


Refer to the chart below for more information about the peak and impacts of the Indian Ocean Dipole.


The Indian Ocean Impacts - For the remainder of the year. It is a general guide and not a rule of thumb but based on current guidance this seems to be fair.

TIMING OF INFLUENCE - GENERAL RULE - NOT FIXED!

WA - You have felt the full impact of those warmer waters through May and June but has eased in recent times, but it will be back through the months ahead.


SA - Starts from later July into August and then peaks in the September/October so the minimal impact so far, seasonal and expected.


VIC - Similar to SA, impacts gradually increase from July onwards and then more prominent through August and into Spring when the nation warms, and the jet stream becomes more wavy sending in the moisture.


NSW - Increasing influence from July onwards but more prominent from August through November, especially on and west of the divide with the dividing range undercutting the influence for the coastal fringe.


QLD - Really impacts the southern third of the state and this starts to be felt from later August through Spring but the easterly winds that return push back a lot of the influence through the state and shoves it southwards for the remainder of central and northern areas, doesn't mean we don't get moisture influence, but it is more frequent the further south you go.


NT - Influence greatest over the western Top End and you should start to see increasing showers and storms from as early as late August and certainly an increase in humidity coming back in about 6-8 weeks.


Blue Zones - High Impact from a negative IOD event.

This area can expect to see above average rainfall chances through July onwards to the end of the year, that's based off the current guidance from the climate models and other data sets I have scoured through in recent days. I am of the belief that the further we go into July, the wetter the phase will get likely to increase through August and September.


Flooding becomes a risk through parts of NSW, VIC and SA with the frequency of the rainfall and the intensity increasing as the nation warms up adding more atmospheric dynamics. That will see the rain become more thundery as well in line with the storm season, so the risk of not only riverine flooding, but flash flooding becomes an issue.


I will be talking more about the flood risks over the coming week for inland areas of QLD, NSW, VIC and SA because this could be on those situations where many who don't get the information could be caught with the pants down around their ankles what the hell is going on.


Light Green Zones - Moderate impact from negative IOD event.

Rainfall has a higher chance of being more frequent and heavier, but the risk of exceeding the average is not as elevated for July. Generally, the rainfall is connected to the westerly wind belt and there are signs that will be present through early July with rainfall for a number of days for the region.


Longer term, the rainfall can be heavier through these regions but generally the above average rainfall risk is slight decreased off climate history. But with the IOD event continues into the late spring and summer, we could see rainfall continue through to the end of the year for interior regions where flooding may develop.


With early onset rainfall further moisture will likely pool from the north and northeast over these regions, not just connected to the Indian Ocean. That is more likely for central and eastern interior regions.


And in the east, an active and very wet storm season is likely to unfold, with not necessarily more severe thunderstorm events, but if forms form, thunderstorms may be more productive and lead to flash flooding events.


Dark green zones - Moderate impact from a negative IOD event.

High chance of more humidity values interrupting the dry season over the coming months with significant chances of pop up showers and storms through the dry season from time to time between July to August.


The build up likely to be earlier through the NT and Cape York and then spreading into the Kimberly. The build up likely to start with a protracted period of higher humidity and not much rainfall then a more active storm season from October through November.


Early onset rainfall is highly likely for large areas (I will have more to say about this is a couple of weeks). This may suppress day time heat indices which are excessive during this period.


The IOD lingering into early summer could elevate the risk of early cyclones over the Indian Ocean in particular ahead of the monsoon developing later in December.


Rainfall looks likely to be above average from October through December through these regions.


FORECAST

Indian Ocean - 9 Month Outlook

The Indian Ocean is forecast to turn more negative (more warmer waters to appear throughout the basin) throughout June into July. The strength of the negative phase is forecast to increase from July into August, and you think it is wet across the eastern inland at the moment? Well, it is about to get wetter if the outlook verifies, and the rainfall will spread to much of SA and through VIC with higher frequency and intensity. So, while the weather is a little dry through some pockets of SA, this is expected to flip as it normally does through late May into June. The negative phase of the IOD is forecast to peak around September through November and the drawn-out phase of the IOD is of concern, with flooding risks increasing through late Winter and into Spring. There is some chance we will not lose the warnings over the inland parts of QLD and NSW throughout the year given the moisture content and rainfall forecasts/observed falls in recent times. The northern tropics will likely see above average temperatures through the dry season, higher humidity and above average rainfall chances and early onset wet season activity from August. This will play out through parts of QLD as well with higher falls for cattle country against seasonal averages through the north and west. In WA, widespread rainfall is forecast to emerge through the Central and Northern Interior along the jet stream which will be dragging in larger and above average rainfall chances. This could at times feed higher moisture content into the SWLD with increased rainfall chances through the southwest wet season. Crops in the east have been drowning in recent weeks and sadly the growing and harvest season is going to be challenging for many locations on this current guide.






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