The Fast Break – Victoria

Seasonal climate risk information for Victoria

Volume 19 | Issue 7 | 27 July 2024

It’s been a drier month in the north, an average to drier month in the southwest and a wetter month in most of Gippsland. Soil moisture was essentially unmoved in most northern areas, became saturated across Gippsland and finally started to increase in the southwest. Soil moisture remains drier than normal across the southwest and has also been decile one in the alps.

In the Pacific Ocean the area of cool water underneath dissipated in the far east and has moved closer to the central Pacific. Many models predict an upwelling of cooler water to occur at the surface of the central Pacific. La Niña’s (potentially wetter) forming in this location have the Japanese term ‘Modoki’.

There has been no stronger easterly trade winds, decreased cloud at the dateline, or lower pressure over Darwin that would suggest the atmosphere is remotely interested in forming a La Niña yet. The Coral Sea to the northeast of Australia remains much warmer than normal at the surface. This would be a better moisture source if stronger easterly trade winds could blow it north of Australia.

The Indian Ocean changed the most over July. Increasingly warmer water built up in the eastern half and some of the western normalised. The Dipole Mode Index started to head into negativity to reflect this difference. A few models are sniffing the possibility of a -IOD (potentially wetter) although no atmospheric indicator (wind, cloud, pressure) is currently showing any interest.

The area of really warm water off Madagascar shrunk, which may be providing a better pressure pattern regime over Australia. The Timer Sea to the north of us is predicted to remain warm for the rest of the season, possibly a better moisture source.

Pressure patterns showed some improvement this month, particularly for the southwest. The overall latitude was further north allowing frontal systems through. The average position of the high over South Australia meant that getting connections to moisture for northern Victoria was challenging.

Models last month were predicting the dominant high to hang around over the Bight, but no model now has a pattern like this. Many models predict lower pressure over Victoria, indicating a position more favourable for rainfall.

The Southern Annular Mode (SAM) had been bouncing around between week negativity and positivity, much as it has all season. Recently the SAM has trended to moderate negativity, and in a classic response there has been frequent frontal activity across southwest Victoria. A negative SAM in winter can push southern ocean frontal systems closer to Victoria.

The Madden-Julian Oscillation (MJO) has been essentially missing in action and is predicted to not be a moisture source for Victoria in the next 30 days.

My assessment of 12 climate models for Victoria is split between neutral and likely wetter. Temperatures are likely to be warmer for the next three months. Model accuracy is moderate at this time of year. A neutral outlook predicts an equal chance of wetter, average or drier.

Soil moisture

Compared to 30 days earlier than 22 July 2024

The BoM Australian Water Outlook decile (AWO) deciles for perennial pasture show most of the southwest are drier at decile 1. The northeast alps are also ranked decile 1. Far east Gippsland is ranked wetter at decile eight to ten. The moisture probe network shows healthy increases in many southern areas where northern probes are stable. The median change of probes that wet up was +33 percentage points. The Lawloit lucerne increased 22 percentage points from 21% to 43% and the Terang dairy pasture increased a whopping 73 points from 19% to 92%.

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

Probes from Agriculture Victoria, Dookie Land Management Group, Gecko Clan, Perennial Pasture Systems, Gippsland Agriculture Group, Murrayville Landcare and Riverine Plains Inc. networks.

Model distribution summary for the next 3 months

Predicted rainfall: August to October 2024

Predictions for August to October 2024, the outlook from 12 global model forecasts for Victorian rainfall is split between neutral and likely wetter. Note that ‘neutral’ means the forecast models show an equal spread of average, drier or wetter eventualities are possible.

Model distribution summary for Victoria

Predicted temperature: August to October 2024

Predictions for August to October 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: November to January 2025

Predictions for November to January 2025, the outlook from nine global model forecasts is split between neutral and likely wetter across Victoria.

Predicted temperature – November to January 2025

Predictions for November to January 2025, the outlook from 9 global model forecasts is for likely warmer across Victoria.

Model consensus forecast for the next 6 months

Current outlook (27 July)

Previous outlook (27 June)

Sea surface temperature (SST) anomalies

The equatorial Pacific Ocean surface was essentially unchanged in July. The oceanic values for NINO3 and NINO3.4 were to +0.07^oC and +0.24^oC respectively (22 July). Both these values are normal. Any attempt to form a La Niña has been stalled. The Coral Sea remains much warmer, and the water off Queensland is normal.

The Indian Ocean has warmed further in the eastern half and backed off closer to normality, with the odd cold outbreak in the western half. The Dipole Mode Index is currently -0.29^oC (22 July). Negative IOD conditions are when the difference between western and eastern box temperatures is -0.4^oC or more.

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

National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch Daily 5 km SST Anomalies (Version 3.1) 25 June 2024.

Equatorial Pacific subsea temperature anomalies

Analysis done 16 July 2024

The Pacific Ocean Equatorial sub-surface temperature area of cool has moved toward the central Pacific. The undersea ocean has gained heat over recent months which is not what we would expect for a La Niña. Many models predict surface cooling above the central cool area in coming months.

Southern Oscillation Index (SOI)

30-day moving SOI

The SOI has remained at neutral values during July, currently at -3.0 (as of 22 July 2024). The slightly negative SOI is due to the pressure having been slightly higher at Darwin.  An SOI above +7, would suggest a switch to La Niña like pressure behaviour, but importantly the pressure would be lower at Darwin.

.

© 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 trending negative (currently -0.29°C at 22 July) due to the eastern box warming up more than the western box. A value less the -0.4 would be like a negative IOD.

© 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 20 June to 19 July.

Equatorial trade winds in the Pacific Ocean and near Sumatra have been normal in July. Movements towards a La Nina are predicated on strengthening of these winds to upwell cooler water and push warmer water to the north of Australia. A -IOD would be predicated on stronger westerly winds off Sumatra pushing warmer water over Indonesia. In the last week there has been some stronger easterly wind in the central Pacific, we will see if this can sustain itself. There has also been stronger easterly wind off Sumatra which is counter to the formation of a -IOD.

(NCEP Operational climatology data: 1985–1996, smoothed with 5-day running mean) Source: NOAA

World cloudiness anomalies

OLR Anomalies: Average of 20 June to 20 July 2024

Cloud patterns around the international dateline junction are normal but there is greater cloud off the warmer waters of the Coral Sea. A La Niña pattern would show much less cloud at the dateline and greater cloud to the north of Australia. The strong convection off Madagascar last month has disappeared. There has been a lack of northwest cloud band activity through the Kimberly.

Source: Bureau of Meterology

Southern Annular Mode (SAM)

AAO: Observed and GFS forecasts

Observations 24 March 2024 to 21 July 2024

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) is currently moderately negative. During July the SAM bounced between negativity and positivity much as it has been since summer. NOAA predicts the SAM to stay negative and the BoM returns it to neutrality in coming weeks. A negative SAM can mean greater frontal activity, particularly for southwest Victoria.

Source: NOAA

Madden Julian Oscillation (MJO)

MJO Phase Diagram for 11 June to 20 July 2024

For July the MJO was mainly missing in action away from Australia. Mid-month it had a brief weak burst into position 5 off Indonesia 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 weakly circulate reaching position 3 in the eastern Indian Ocean in 30 days’ time. Its unlikely to be a moisture source if this eventuates.

Source: Bureau of Meterology

Air pressure

Last 30 days air pressure

Operational data: Sea level pressure (mb) 30-day mean for: Thursday 20 June to Friday 19 July 2024.

In the past 30 days the Sub Tropical Ridge of High Pressure (STR) has been centred over central Australia. This has allowed frontal systems to sneak past south of the Divide but has been blocking systems north of the Divide.

Source: NOAA

Air pressure anomalies

Last 30 days air pressure anomaly

Operational data: Sea level pressure (mb) 30-day anomaly for: Thursday 20 June to Friday 19 July 2024.

The Sub Tropical Ridge was higher in pressure south of Australia. This was due to a couple of large high pressures further south than is normal for winter. Pressure is normal at Tahiti but slightly higher at Darwin. This is why the SOI is slightly negative. The area of lower pressure off Madagascar has broadened to be over much of the western and central Indian Ocean.

(NCEP Operational climatology data: 1985–1996, smoothed with 5-day running mean). Source: NOAA

Climate definitions

Read a list of climate acronyms and explanations.

Modelled climate and ocean predictions for Victoria from July 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 (WORD - 75.2 KB)

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

Four coupled global circulation model forecasts

*ASO = August, September, October OND = October, November, December NDJ = November, December, January

Three ensembles and a statistical model forecast

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 which has a public domain policy. Annotations highlighting areas of interest have been added by Dale Grey.