The Fast Break – Victoria

Seasonal climate risk information for Victoria

Volume 19, Issue 5, 27 May 2024

It has been another drier month to date across the whole state with Mallee, Wimmera and east-Northeast regions receiving less than 10mm so far. As we go to print there are hopes of an opening rain at the end of this month. A fluky rain of 20-30mm though north central areas 2 weeks ago ensured germination finally occurred. Mallee and Wimmera crops are essentially waiting for rain whilst southwest and northeast crops are variable in the quality of germination. Pastures in the west Southwest and east northeast are poorer whilst west Gippsland is good but central and east Gippsland could do with a drink. This is evidenced by some perennial pasture paddocks showing significant water use this month where southwest probes are atypically low for this time of the year.

The Pacific Ocean surface is starting a cool wiggle in the east, which is normal as a La Niña tries to establish. The cooler water is upwelling due to a cooler ocean underneath. The atmosphere across the Pacific is close to normal with pressure patterns and winds unconvincing. In the last week some trade wind strengthening has occurred in the central Pacific. More of this would be needed to kick of a proper event. The warm Coral Sea region is producing more cloud from the warmer water, and this is a long standing hang over from the three La Niña’s of 2020-22.

The Indian Ocean has rewarmed around the Sumatran area and remains very warm off Africa. Atmospherically this African warmth at the surface and depth is leading to greater cloud and lower pressure in that region. Off Sumatra less cloud exists but pressure and trade wind activity are closer to normal. So far, the large high-pressure systems have been further south and stronger easterly wind that can form at Sumatra as a result of them, has not eventuated. At this stage the predicted +IOD has more work to do than the predicted La Niña. Its also fair to say that a combination of +IOD (usually drier) and La Niña (usually wetter) is very rare, and the mixture of forecasts for the coming three months reflects this.

The southern annual mode hasn’t been doing a lot, mainly neutral and both positive and negative in the last month. It’s hard to blame it for the later start to the season. Once we reach winter this climate driver has an ability to be more active particularly for southwest Victoria.

The Madden Julian Oscillation is also going missing in action, currently stationed in the central Indian Ocean. It’s predicted to make no further headway eastwards as a moisture source for Victoria for the next month.

Pressure patterns have been unhelpful for rainfall. A high-pressure pattern sat most of the month over Adelaide and steered most frontal systems under and away from the state. The absolute pressure was very high with one high averaging an eye popping 1043 hPa and taking two weeks to move, and the one that followed it wasn’t much better. Clearly a change to this pattern is needed before any start can occur. All eyes are looking hopeful at the forecast at the end of this week which finally sees the pressure moving further north and some space developing between the highs for frontal systems to sneak up and across. It’s likely the low pressure off east Africa and the high pressure over southern Australia are linked.

My assessment of 12 climate models for Victoria is unchanged with mixed rainfall predictions (i.e. plan for anything) (but more than half the models continue the prediction of a likely drier southwest), with likely warmer temperatures for the next three months. Model accuracy is moderate to low for the winter period.

Soil moisture

Compared to 30 days earlier than 27 May 2024

The BoM Australian Water Outlook decile (AWO) was unavailable this month. Soil moisture has decreased in some perennial pastures with a median decline of 14 percentage points. All other probes are not significantly changed with rainfall only at the surface. Evaporation in crop paddocks was a median value of −2 percentage points. The Baynton phalaris decreased 19 percentage points from 79 to 60% and the Buchan perennial pasture decreased 16 percentage points from 27 to 11%.

Soil moisture probe data can be accessed in real time at Agriculture Victoria’s soil moisture monitoring website.

Model distribution summary for the next 3 months

Predicted rainfall: June to August 2024

Predictions for June to August 2024 – the outlook from 12 global model forecasts victorian rainfall is mixed, but a likely drier south-west.

Model distribution summary for Victoria

Predicted temperature: June to August 2024

Predictions for June to August 2024 – the outlook from 11 global model forecasts is for likely warmer across Victoria.

Model distribution summary for the next 4 to 6 months

Predicted rainfall: September to November 2024

Predictions for September to November 2024 – the outlook from 9 global model forecasts is split between likely wetter rainfall and neutral.

Predicted temperature – September to November 2024

Predictions for September to November 2024 – the outlook from 9 global model forecasts is for likely warmer across Victoria.

Model consensus forecast for the next 6 months

Current outlook (27 May)

Previous outlook (23 April)

Sea surface temperature (SST) anomalies

The Equatorial Pacific Ocean surface has slowly cooled further> in May. The oceanic values for NINO3 and NINO3.4 are +0.02^oC and +0.35^oC respectively (23 May). A long finger of cool water is progressing out from South America. This is to be expected as the Pacific Ocean attempts to form a La Niña. The Coral Sea moisture zone to the northeast is warmer and remains switched on. The Indian ocean is warm right across the basin and the Sumatran area has re-warmed. Water under the eastern box has changed from being cooler to more normal and the cold anomaly has shifted to the central Indian Ocean. It would appear the eastern zone of the +IOD has some work to do to go cold. The Dipole Mode Index has returned from +IOD like values, to +0.20 ^oC, which is neutral.

Sea surface temperatures are the key to the world’s rainfall. For more information on how they are measured, maps created and how to read them, check out our eLearn

Equatorial Pacific sub-sea temperature anomalies

Analysis done 23 May 2024

The Pacific Ocean Equatorial subsurface temperature area of cool water contracted somewhat in May. Cooler water is starting to upwell at the surface. This large slug of cool water to depth is on of the main measurements that models are using to predict a La Niña.

Southern Oscillation Index (SOI)

30-day moving SOI

The SOI is close to zero and at a neutral value in May, currently at +1.1 (as of 25 May 2024). This indicates pressure at Tahiti and Darwin are relatively normal. If pressure started to lower to our tropical north and increase at Tahiti, the SOI would rise above +7, which would suggest a switch to La Niña like pressure behaviour.

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© Copyright Commonwealth of Australia 2024. Bureau of Meteorology

Dipole Mode Index (DMI)

The DMI is the difference between the temperature of the west and east boxes of ocean monitored for the IOD. The DMI is neutral at +0.2^oC. Southeasterly winds during early May haven’t really helped to cool the Sumatran region but have affected off Java.

© Copyright Commonwealth of Australia 2024. Bureau of Meteorology.

Pacific Ocean surface wind anomalies

Wind direction and strength anomalies for the last 30 days

Surface winds (m/s) 30-day anomaly for: Monday 20 May 2024 to Sunday 26 May 2024.

Equatorial trade winds in the Pacific Ocean have been normal for the first three weeks of the month but have recently experienced a burst of slightly stronger easterly in the central Pacific. Without further stronger easterly trade winds in the central Pacific, a La Niña is going to struggle to form. A small area of stronger easterly wind off Sumatra is not convincing of an attempt to kick of a +IOD. Stronger easterly wind off Sumatra would be expected to upwell cooler water in that region. The monsoonal winds in the northern Indian Ocean appear to have finally switched to southwest in the last week. This indicates the southern Indian Ocean might be better able to express itself from now on.

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(NCEP Operational climatology data: 1985 -1996, smoothed with five-day running mean) Source: NOAA

World cloudiness anomalies

OLR Anomalies: Average of 25 April 2024 to 25 May 2024

Cloud patterns around the international dateline junction and the broader equatorial Pacific are weakly less than average. A La Niña pattern would show much less cloud at the dateline. Extra cloud exists northeast of Australia in keeping with the much warmer water in the Coral Sea. A large area of less cloud in the eastern Indian Ocean and greater cloud off east Africa is in a +IOD like pattern, but this could change if cloud starts matching the underlying warm surface ocean temperature across the Indian Ocean.

Source: Bureau of Meterology

Southern Annular Mode (SAM)

AAO: Observed and GFS forecasts

Observations 18 December 2023 to 15 April 2024

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) is currently weakly negative. During May the SAM was mainly neutral with 2 brief forays into moderate negativity and positivity. Once we get to winter, SAM becomes a more reliable climate indicator, particularly for southwest Victoria. Both the Bureau of Meteorology and NOAA predict a weak to moderate negative pitch that returns to neutral in a fortnight.

Source: NOAA

Madden Julian Oscillation (MJO)

MJO Phase Diagram for 16 April 2024 to 25 May 2024

In the first 15 days of May the Madden Julian Oscillation (MJO) was undefined. In the last 10 days it appeared in the western Indian Ocean at weak strength and has been making its way to the central Indian Ocean. The MJO can be a moisture source in positions 5 and 6 if we get a front or low-pressure system to connect into it. The BoM ACCESS model predicts the MJO to die to undefined and not pass north of Australia for the next 30 days.

Air pressure

Last 30 days air pressure

Sea level pressure (mb) 30-day mean for: Monday 20 May 2024 to Sunday 26 May 2024.

In the past 30 days the Sub Tropical Ridge of High Pressure (STR) has been in a summertime latitude and was yet to move further north. At the time of writing the pressure has moved north to a more normal position and looks set to let some rain bearing systems through. The position of the high centred over South Australia is a classic block to frontal systems passing across the state.

Source: NOAA

Air pressure anomalies

Last 30 days air pressure anomaly

Sea level pressure (mb) 30-day anomaly for: Monday 20 May 2024 to Sunday 26 May 2024.

The Sub Tropical Ridge was much higher in pressure over the whole of southern Australia. Some exceptionally strong highs have been moving stubbornly slowly across the state. This had led to weeks of stable weather at a time. Pressure is normal at Tahiti but starting to increase south of there and normal at Darwin but starting to increase there too. This is why the SOI has flipped to a positive albeit neutral value. Pressure is very low off east Africa commensurate with warmer water and greater cloud. There is a high likelihood that the east African low pressure is causing the strong high over southern Australia.

(NCEP Operational climatology data: 1985 – 1996, smoothed with five-day running mean). Source: NOAA

Climate definitions

Read a list of climate acronyms and explanations.

Modelled climate and ocean predictions for Victoria from May 2024 run models

Twelve climate models show their predictions for the next 6 months for the Pacific Ocean, Indian Ocean, rainfall and temperature for Victoria.

View a colour-coded version of this table Modelled climate and ocean predictions for Victoria from May 2024 run models (WORD - 75.3 KB)

Our e-learning module How to read the Fast Break table explains this table.

Four coupled global circulation model forecasts

*JJA = June, July, August  *ASO = August, September, October  * SON = September, October, November

Four coupled global circulation model forecasts

*MJJ = May, June, July  *JJA =June, July, August  *ASO = August, September, October  * SON = September, October, November

Three ensembles and a statistical model forecast

*JJA =June, July, August  *ASO = August, September, October *SON = September, October, November

Image references

Original images used in this document are sourced from the Bureau of Meteorology under a Creative Commons 3.0 licence and from the NOAA who have a Public Domain policy. Annotations highlighting areas of interest have been added by Dale Grey.