The Fast Break – Victoria

May has been drier than average to date in most areas except for the southwest coastal fringe, east Melbourne to West Gippsland, and far east Gippsland.

April rain allowed some early sown crop and pasture to germinate but low rainfall, wind and frosts have dried the surface so much that further rains are now needed to support germination in the northwest and northern country. Southwest and east-northeast regions are ideal. Soil moisture probes only rose significantly in those areas with close to average rainfall.

The Pacific Ocean sea surface temperatures are in a weak El Niño condition in the east but a neutral condition in the central region, which is believed to affect Victoria more. The western Pacific still remains very warm at the surface and at depth as a good moisture source but ways of getting it down from there have been hard to find.

The Pacific atmosphere has shown limited to no interest in coupling with the ocean. Cloud, wind and pressure patterns have been normal but in the last 10 days the pressure has increased at Darwin and there is a weak burst of westerly wind off the Solomon Islands. Both these will be worth watching if they continue, as it will indicate a chance for the atmosphere to couple.

Classic El Niño effects tend to only occur if the system is coupled. If the current burst of the Madden Julian Oscillation (providing the reversed trade winds) fails to kick of central Pacific warming or western cooling it will be another 40 or so days before it gets another chance. All models surveyed predict a central Pacific El Niño to form and hang around for at least six months.

The Indian Ocean is poised to be a positive Indian Ocean Dipole but currently only at depth. The ocean surface is currently warmer or normal and stronger easterly winds off Sumatra have been short lived to get the colder water to up-well. Cloud and pressure patterns have been more in keeping with the MJO rather than the underlying ocean conditions. Keep an eye on the big high-pressure systems as a really big one could provide enough easterly wind in the Timor Sea to flip it over cool. Nearly all models predict a +IOD to form and hang around till November.

While El Niño and +IOD historically give greater chances of drier and warmer conditions, the model predictions are predicated on these climate drivers actually forming and coupling. It they don’t, the rainfall outcomes are more uncertain.

The Southern Annular Mode (SAM) has been moderate to strongly positive over May and appears to be dragging weather systems south particularly north of the divide. It is predicted to behave itself at normality in coming weeks.

Unusually with a +SAM, the Sub Tropical Ridge of high pressure has been at a favourable latitude for allowing fronts up, but probably only benefitting southern areas. The actual pressure has been slowly increasing, which is probably the key factor to why rain has been hard to find in the north.

My assessment of 11 climate models for Victoria shows a likely drier rainfall and likely warmer temperatures for the next three months.

Soil moisture

Compared to 30 days earlier than 22 May 2023

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

The Australian Water Outlook (AWO) predicts Victoria has slightly dried out in the north but is unchanged in the south. The northwest and northern country are ranked drier and below average, the alps and far southwest are ranked above average. Probes show little change for the month, most with single figure decreases. The Jancourt perennial pasture rose 24 percentage points from 39 to 63 % and the Brim crop decreased by eight percentage points dropping from 88 to 80 %.

Map of Victoria showing modelled plant available moisture (%). Most probes are unchanged, only two southern ones have risen.

+ Expand all- Collapse all

Jancourt perennial rye

63

Longwarry chicory

100

Giffard crop

77

Brim crop

80

Greta phalaris

88

Goorambat crop

93

Elmore crop

62

Yalla-Y-Poora crop

81

Baynton granite annual

40

Baynton granite phalaris

81

Rutherglen crop

96

Raywood annual

51

Greta annual pasture

96

Paradise perennial

50

Baynton basalt phalaris

74

Greta summer pasture

97

Taylors Lake crop

98

Strathbogie pasture

55

Sheep Hills crop

67

Birchip crop

73

Coonooer Bridge crop

100

Normanville crop

100

Ouyen crop

100

Speed crop

100

Werrimull crop

100

Youanmite crop

100

Dartmoor lucerne

100

Pigeon Ponds ryegrass and balansa

100

Glenlofty perennial

46

Lawloit lucerne

21

Hamilton crop

63

Bairnsdale perennial

62

Nil

Model distribution summary for the next 3 months

Predicted rainfall – June to August 2023

Predictions for June to August 2023, the outlook from 11 global model forecasts is for likely drier across Victoria.

Graph showing one neutral/drier and ten drier forecasts for June to August 2023 Victorian rainfall.

Model distribution summary for Victoria

Predicted temperature – June to August 2023

Predictions for June to August 2023, the outlook from 10 global model forecasts is for likely warmer across Victoria.

Graph showing ten warmer forecasts for June to August 2023 Victorian temperature.

Model distribution summary for the next four-to-six months

Predicted rainfall – September to November 2023

Predictions for September to November 2023, the outlook from eight global model forecasts is for likely drier over Victoria.

Graph showing one neutral, and seven drier forecasts for September to November 2023 Victorian rainfall.

Predicted temperature – September to November 2023

Predictions for September to November 2023, the outlook from eight global model forecasts is for likely warmer across Victoria

Graph showing eight warmer forecasts for September to November 2023 Victorian temperature.

Model consensus forecast for the next 6 months

Current outlook (24 May 2023)

Phenomena

June – August 2023

September – November 2023

Pacific Ocean

Warm (El Niño)

Warm (El Niño)

Indian Ocean

Cooler (+IOD)

Cooler (+IOD)

Rainfall

Drier

Drier

Temperature

Warmer

Warmer

Previous outlook (27 April 2023)

Phenomena

May – July 2023

August – October 2023

Pacific Ocean

Warm (El Niño)

Warm (El Niño)

Indian Ocean

Cooler (+IOD)

Cooler (+IOD)

Rainfall

Drier / Neutral

Neutral / Drier

Temperature

Warmer

Warmer

Sea surface temperature (SST) anomalies

National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch Daily 5 km SST Anomalies (Version 3.1) 20 May 2023.

The Equatorial Pacific Ocean has warmed further during May. The oceanic values for NINO3 and NINO3.4 are +1.02oC and +0.55oC respectively (as of 24 May). NINO3 is above the El Niño threshold of 0.8 oC but NINO 3.4 is lagging behind and remains neutral.

Waters to our northeast remain very warm as a legacy of the La Niña. The Indian Ocean is neutral and the (DMI) is -0.15oC, which is normal for this time of the year. It will be important to watch the cooling in the Timor Sea to our northwest for further propagation eastwards and northwards.

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.

Map of the world showing sea surface temperature anomalies, an El Niño is extending out from the Ecuadorian coast, but the central equatorial Pacific Ocean is only slightly warm. There is a very warm Coral Sea to the north-east and the Indian Ocean is warmer in the west and normal in the east.

Equatorial Pacific sub-sea temperature anomalies

Analysis done 18 May 2023

The Pacific Ocean Equatorial sub-surface temperatures have warmed further with an eastern Pacific warm upwelling, but no central Pacific warming to depth yet.

Cross section of the Equatorial Pacific Ocean chart showing a consolidating area of warmer water to depth in the eastern Pacific and a large area of warmer water remaining in the western Pacific. Cross section of the Equatorial Pacific Ocean chart showing a large area of cooler water to depth in the eastern Pacific.

Southern Oscillation Index (SOI)

30-day moving SOI

The SOI has declined into negativity during May, currently at -7.9 (as of 20 May 2023). Pressure patterns around the equator are close to an El Niño value of -8.0.

Graph of the SOI shows the value is currently at -7.9

© Copyright Commonwealth of Australia 2023. 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 has stayed at normal values for May. A +IOD value would be above + 0.4 oC.

Graph of the DMI shows the value is currently at -0.15oC

© Copyright Commonwealth of Australia 2023. 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 22 April 2023 to Sunday 21 May 2023.

The Pacific Ocean easterly trade winds are at normal values. The beginnings of a potential pulse of westerly wind have recently appeared north of PNG and the Solomon Islands. El Niño behaviour would be indicated by continued westerly wind off the Solomon Islands in the western Pacific.

The eastern Indian Ocean shows normal winds, although a brief but unsustained week of easterly wind occurred mid-month. Positive IOD behaviour would be consistent easterly wind off Sumatra in the eastern Indian Ocean.

These two regions are the key indicators for either El Niño’s and/or +IOD development this season.

Map showing normal equatorial Pacific Ocean and Indian Ocean winds.

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

World cloudiness anomalies

OLR Anomalies: Average of 20 April 2023 to 20 May 2023

Cloud over the international dateline junction with the equator is now normal. This was the last indicator to retreat from La Niña values for the first time in eight months. Greater cloud exists over PNG associated with the warm water in that region and a pulse of the Madden Julian Oscillation. There has been less cloud over Victoria.

Map of the world showing normal cloud at the equatorial junction with the dateline and some greater cloud over PNG.

Source: Bureau of Meterology

Southern Annular Mode (SAM)

AAO: Observed and GFS forecasts

Observations 22 January 2022 to 21 May 2023

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) went strongly positive in May. SAM’s behaviour in autumn can be erratic and has a poor correlation with rainfall but due to the closeness of winter it is tempting to correlate the drier conditions with weather systems being pulled south by this climate driver. The Bureau of Meteorology and NOAA both predict the SAM to return to neutral in a week and remain there for the next week.

Graph of the SAM showing strong positive values during May.

Source: NOAA

Air pressure

Last 30 days air pressure

Operational data: Sea level pressure (mb) 30-day mean for: Saturday 22 April 2023 to Sunday 21 May 2023.

In the past 30 days, the Sub Tropical Ridge of High Pressure (STR) remained in a normal to slightly higher latitudinal position for autumn centred near the top of the Bight. The pressure which had been building from the west is now positioned over the whole of southern Australia on average.

The latitude of the pressure ridge is far enough north to be allowing fronts through, particular south of the divide. The extent of the high pressure has not been enough to drastically overturn the Timor sea cooler.

Map of the world showing the STR of high pressure at a normal to more northerly position than normal.

Source: NOAA

Air pressure anomalies

Last 30 days air pressure anomaly

Operational data: Sea level pressure (mb) 30-day anomaly for: Saturday 22 April 2023 to Sunday 21 May 2023.

The STR gained pressure over May meaning high pressure systems were more dominant and slower moving. This has a fair bit to do with the drier weather over May. Pressure was also increasing to our tropical northeast and into Darwin, with slightly lower pressure at Tahiti. This is why the SOI is positive.

Map of the world showing higher pressure extending from the west over Victoria.

(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 2023 run models

Twelve climate models show their predictions for the next six 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 2023 run models (WORD - 67.5 KB)

Our new e-learn explains this table.

Four coupled global circulation model forecasts

* Abbreviations:

JJA = July, August, September

ASO = August, September, October

SON = September, October, November

Phenomena

System 5
ECMWF
Europe

ACCESS-S
BoM
Australia

SINTEX-F
JAMSTEC
Japan

CFSv2
NCEP
USA

Month of Run

May

May

May

May

Forecast months*

JJA

JJA

JJA

JJA

Rainfall Skill MJJ

Moderate

Moderate

-

Low / Moderate NC

Winter Pacific
Ocean NINO3.4

Warm
(El Niño)

Warm
(El Niño)

Warm
(El Niño)

Warm
(El Niño)

Winter Eastern
Indian Ocean

Cool (+IOD)

Cool (+IOD)

Cool (+IOD)

Normal

Winter Rainfall

Slightly drier, drier NE

Drier N, slightly drier S

Slightly drier

Slightly drier W, neutral E

Winter Temperature

Slightly warmer, neutral NE

Warmer

Slightly warmer

Slightly warmer, neutral NW

Forecast months*

SON

ASO

SON

SON

Spring Pacific
Ocean NINO3.4

Warm
(El Niño)

Warm
(El Niño)

Warm
(El Niño)

Warm
(El Niño)

Spring Eastern
Indian Ocean

Cool (+IOD)

Cool (+IOD)

Cool (+IOD)

Normal (weak +IOD)

Spring Rainfall

Slightly drier

-

Slightly drier

Slightly drier, neutral far E

Spring Temperature

Slightly warmer, warmer Mallee, Gipps

-

Slightly warmer

Slightly warmer

Further Info

Operational

Operational

Experimental

Operational

Four coupled global circulation model forecasts

* Abbreviations:

JJA = July, August, September

ASO = August, September, October

SON = September, October, November

Phenomena

GEOS-S2S
NAS
USA

EPS
JMA
Japan

CSM1.1m
BCC
China

GloSea5
UKMO
UK

Month of Run

May

May

May

May

Forecast months*

JJA

JJA

JJA

JJA

Rainfall Skill MJJ

-

Moderate

-

Moderate

Winter Pacific Ocean NINO3.4

Warm
(El Niño)

Warm
(El Niño)

Warm
(weak El Niño)

Warm
(El Niño)

Winter Eastern
Indian Ocean

Cool (+IOD)

Cool (+IOD)

Cool (+IOD)

Cool (+IOD)

Winter Rainfall

NA

Drier N, slightly drier S

Slightly drier

Drier

Winter Temperature

Slightly warmer

Neutral

Warmer

Slightly warmer, warmer NW

Forecast months*

SON

-

SON

ASO

Spring Pacific Ocean NINO3.4

Warm
(El Niño)

-

Warm
(El Niño)

Warm
(El Niño)

Spring Eastern
Indian Ocean

Cool (+IOD)

-

Cool (+IOD)

Cool (+IOD)

Spring Rainfall

NA

-

Slightly drier

Drier W, slightly drier E

Spring Temperature

Slightly warmer

-

Warmer

Warmer

Further Info

Experimental

Experimental

Operational

Operational

Three ensembles and a statistical model forecast

* Abbreviations:

JJA = July, August, September

ASO = August, September, October

SON = September, October, November

Phenomena

NMME
USA

C3S
Europe

MME
APCC
Korea

SOI phase
USQ/Qld
Australia

Month of Run

May

May

May

May

Forecast months*

JJA

JJA

JJA

JJA

Rainfall Skill MJJ

Moderate / Low ESW

-

-

-

Winter Pacific Ocean NINO3.4

Warm
(weak El Niño)

Warm
(weak El Niño)

Warm
(El Niño)

SOI falling

Winter Eastern

Indian Ocean

Cool (weak +IOD)

Cool (weak +IOD)

Cool (+IOD)

-

Winter Rainfall

Drier

Drier N, slightly drier S

Drier N, slightly drier S

Slightly drier, neutral E Gipps

Winter Temperature

Slightly warmer

Slightly warmer N, warmer S

Warmer

-

Forecast months*

SOn

ASO

SON

-

Spring Pacific Ocean NINO3.4

Warm
(El Niño)

Warm
(El Niño)

Warm
(El Niño)

-

Spring Eastern
Indian Ocean

Cool (+IOD)

Cool (+IOD)

Cool (+IOD)

-

Spring Rainfall

Slightly drier

Slightly drier

Slightly drier

-

Spring Temperature

Warmer

Warmer

Warmer

-

Further Info

Experimental
Summary of 8 dynamic models

Experimental
Summary of 9 dynamic models

Experimental
Summary of 13 dynamic models

5 phase system based on previous 2 months SOI

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.

Page last updated: 24 May 2023