The Fast Break – Victoria

Seasonal climate risk information for Victoria

Volume 19 | Issue 10 | 24 October 2024

It’s been another drier month in most of the southwest and also in East Gippsland, with just the Mallee and the Corio region being wetter.

Soil moisture has risen from the stormy rain at a few locations that delayed the onset of barley harvesting and halted hay baling in the Mallee. Most Mallee crops have stopped water use as crops are close to maturity. Some crops will be leaving soil moisture behind as root growth was too shallow to access deeper reserves. Perennial pasture soil water is declining in the southwest as water use is greater than what rainfall provided.

The Pacific Ocean is still only around halfway towards any potential La Niña forming. Some stronger easterly trade winds have helped it to cool further, but there doesn’t seem to be a willingness for these winds to be sustained to further develop an event. Coupling between the ocean and atmosphere is poor. Cloud has decreased at the Date Line but is not yet increasing in northern Australia. Pressure patterns are also not reflecting La Niña-like behaviour.

The Indian Ocean rapidly warmed off Sumatra on the back of a burst of stronger westerly wind, but this has not been sustained. Despite the Dipole Mode Index (DMI) indicating strong negative (−IOD) like values, this is being driven primarily by temperatures off Sumatra rather than any definite cooling off east Africa. Also, the atmosphere in terms of pressure, winds and cloud shows zero coupling with the warmer water off Sumatra. The northern wet season usually kicks in around November and this rapidly neutralises any atmospheric IOD pattern that has established in the Indian Ocean. A lot of models predict a broad warming in the eastern Indian Ocean and neutral to cooler water in the western Indian Ocean, with only 2 models predicting a classic ‘eye’ of warming off Sumatra.

The Southern Annular Mode (SAM) spent October in neutrality or weak negativity. SAM has less influence over frontal positioning in spring and starts to exert more influence on eastern Victorian moisture processes.

The Madden–Julian Oscillation (MJO) passed through the important moisture source positions 5 (north-west of Australia) and 6 (north-east) of Australia during October. It’s likely the one major rainfall event experienced in October got a northern tropical connection when joined with the MJO. The MJO is predicted to take the next 30 days to get back to the central Indian Ocean.

Pressure has once again been causing issues, with the high-pressure ridge yet to make its southwards migration and sitting more at a winter pattern at the top of the Bight. Plenty of fronts have passed across the state but not a lot of rainfall emanated. Pressure was higher over Victoria too, meaning systems were slower moving.

My assessment of 12 climate models for Victoria is split between increased chances of being wetter and neutral (anything could happen), although our confidence in the wetter forecasts is low, given the poor form of models in recent months. Temperatures are likely to be warmer for the next 3 months.

Soil moisture

Compared to 30 days earlier than 28 October 2024

The BoM Australian Water Outlook (AWO) deciles for perennial pasture rank average or drier with the exception of the Mallee and far southwest corner, which are ranked wetter. The soil moisture probe network shows 2 locations picking up some patchy storms where most of the northern crops have ceased to use water due to crop senescence. South-west pastures continue to use water faster than monthly rainfall, while conditions are mixed in Gippsland. The median change of probes that dried in the past month was −18 percentage points. The Cowangie crop increased 11 percentage points from 45% to 67% and the Omeo permanent pasture decreased 18% from 46% to 28%.

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: November 2024 to January 2025

Predictions for November 2024 to January 2025, the outlook from 12 global model forecasts is split between likely wetter and neutral across Victoria.

Model distribution summary for Victoria

Predicted temperature: November 2024 to January 2025

Predictions for November 2024 to January 2025, 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: February to April 2025

Predictions for February to April 2025, the outlook from ten global model forecasts is for likely wetter across Victoria.

Predicted temperature: February to April 2025

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

Model consensus forecast for the next 6 months

Current outlook (28 October)

Previous outlook (23 September)

Sea surface temperature (SST) anomalies

The equatorial Pacific Ocean surface cooled further over October in the central region. The oceanic values for NINO3 and NINO3.4 were −0.22 and −0.53^oC respectively (28 October). Both these values remain normal. A La Niña value would be cooler than −0.8 ^oC. Ocean temperatures are warmer than normal across the northern Australian seas as better moisture sources. Most models predict a La Niña forming in the central Pacific, a flavour of La Niña called a ‘Modoki’.

The Indian Ocean has rapidly warmed off the coast of Sumatra and remains normal to warmer off Africa. The Dipole Mode Index is currently −0.93^oC (28 October), a strongly negative-IOD-like value, but most of this signal is coming from Sumatra, not in conjunction with Africa.

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) 26 October 2024.

Equatorial Pacific subsea temperature anomalies

Analysis done 24 October 2024

The Pacific Ocean Equatorial subsurface temperature stayed at a similar size, but backed off in terms of coolness during October. This looks like a weaker pre-La Niña pattern. Cooler water has started to upwell in the central Pacific.

Southern Oscillation Index (SOI)

30-day moving SOI: 25 October 2024

The SOI remained stationary for October at neutral values. The SOI is currently at +4.1 (as of 28 October 2024). The tropical atmosphere has been showing little interest in La Niña, where values above +8 would be more like La Niña.

© Copyright Commonwealth of Australia 2024. Bureau of Meteorology. Climatology period 1933–92.

Dipole Mode Index (DMI)

Latest weekly value to 20 October 2024

The DMI is the difference between the temperature of the west and east boxes of ocean monitored for the IOD. The IOD is at a strongly negative IOD like value (currently −0.93^oC on 20 October). The majority of this signal is coming from a very warm eastern box.

© Copyright Commonwealth of Australia 2024. Bureau of Meteorology.

Pacific Ocean surface wind anomalies

Wind direction and strength anomalies for the last 30 days

Operational data: Surface winds (m/s) 30-day anomaly for: Saturday 28 September to Sunday 27 October 2024.

Further bursts of stronger easterly trade wind in the Pacific Ocean during October have helped to slightly increase the coolness in the central region. Continued stronger easterly wind is needed to maintain and enhance any La Niña response. In the Indian Ocean, a burst of stronger westerly wind in the central Indian Ocean made its way over to Indonesia. This has caused the ocean to build up warmer off the island of Sumatra in a −IOD like pattern. Sustained stronger westerly wind would be needed to maintain this.

(NCEP Operational climatology data: 1985–96, smoothed with 5-day running mean.) Source: NOAA.

World cloudiness anomalies

OLR anomalies: Average of 26 September to 26 October 2024

Cloud at the junction of the Date Line is less than normal, which is more like a La Niña. Normally greater cloud would exist north of Australia and this is not apparent. Over in the central Indian Ocean a large region of greater cloud exists due to the warmer water under that area.

Source: Bureau of Meteorology.

Southern Annular Mode (SAM)

AAO: Observed and GFS forecasts

1 July to 29 October 2024

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) has been mainly neutral with weak bursts of negativity at the start and end of October. SAM ceases to be a northern pusher or southern puller of storms in spring and summer. A negative SAM can lead to less easterly moisture flow into the east of Victoria. In the next 14 days BoM predicts a neutral phase moving into a sustained weak positivity and NOAA predicts a weak negative phase before returning to neutral values.

Source: NOAA.

Madden–Julian Oscillation (MJO)

MJO Phase Diagram for 17 September to 26 October 2024

For October the MJO cloud band weakly formed east of Africa then made a stronger rush across northern Australia in the last fortnight. It’s probable the rainfall event of 18 and 19 October got a source of moisture out of the MJO when it was north of Australia. The BoM ACCESS model predicts the MJO to spend the next 30 days traversing the Pacific and arriving in the central Indian Ocean with no strength. It’s predicted to pass through the central Pacific with some strength, which might inhibit further cooling of the central Pacific.

Source: Bureau of Meterology.

Air pressure

Last 30 days air pressure

Sea level pressure (mb) 30-day mean for Saturday 28 September to Sunday 27 October 2024.

In the past 30 days the Sub Tropical Ridge of High Pressure (STR) has been further north of a normal spring position of Adelaide. This is has meant plenty of frontal activity passing by, but connections to the tropics were only made once. Victoria has spent a lot of time placed in between highs off WA and east of New Zealand.

Source: NOAA.

Air pressure anomalies

Last 30 days air pressure anomaly

Sea level pressure (mb) 30-day anomaly for Saturday 28 September to Sunday 27 October 2024.

The Sub Tropical Ridge was slightly higher in pressure over Victoria during October, meaning pressure was slower moving and spent more time blocking. Pressure was normal at Darwin and slightly higher at Tahiti. This is why the SOI is a normal value. A La Niña would form much lower pressure at Darwin.

(NCEP Operational climatology data: 1985–96, 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 October 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 - 76.9 KB)

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

Four coupled global circulation model forecasts

*NDJ = November, December, January; DJF = December, January, February; FMA = February, March, April; MAM = March, April, May

Four coupled global circulation model forecasts

*NDJ = November, December, January; JFM = January, February, March; FMA = February, March, April

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.