Weekly update - 11 May 2023

For the week ending 10 May 2023, high-pressure systems kept much of Australia clear and dry. However, a series of cold fronts moved across the south-east of the country, bringing frosty conditions to southern parts of Australia and showers in southern Victoria, southeast New South Wales, southern South Australia and western Tasmania. Troughs brought isolated showers and storms in southwestern Western Australia and the far north of Queensland.

Little to no rainfall was recorded for most cropping regions, except for some northern Western Australia regions which received rainfall totals of up to 25 millimetres. The predominately dry conditions will have aided the finalisation of summer crop harvest for both northern and southern cropping regions. Where soil moisture levels allowed, the mostly dry conditions would have encouraged increased winter crop planting activity, with many growers eager to complete planting programs within the ideal planting window

Rainfall for the week ending 10 May 2023

The climate drivers with the largest potential impact on Australia’s climate patterns are the El Niño–Southern Oscillation (ENSO), Madden-Julian Oscillation (MJO), Indian Ocean Dipole (IOD) and Southern Annular Mode (SAM). These climate drivers are likely to influence harvest progress of later planted summer crops in northern growing regions, pasture growth across both northern and southern Australia, and planting opportunities and the establishment and growth for winter crops.

The Madden–Julian Oscillation (MJO) pulse is currently over the Maritime continent and is forecast to move into the western Pacific region. At this time of the year MJO has little influence on northern Australia rainfall. However, an MJO pulse over the western Pacific would likely weaken trade winds across the equatorial Pacific Ocean. This, in turn, would result in further warming of the equatorial Pacific Ocean and hence drive further development towards El Niño.

The ENSO is in its neutral phase with both oceanic and atmospheric indicators having returned to neutral levels. Oceanic indicators are measured in terms of the sea surface temperature (SST) anomalies. The weekly difference from average SST between 1 to 7 May the SST were warmer than average over the eastern equatorial Pacific Ocean, with anomalies over 4°C in the far east. The atmospheric indicators are measured in terms of the surface air pressure difference between Tahiti and Darwin, called Southern Oscillation Index (SOI). For the period ending 8 May 2023, the 30-day SOI was -2.2 and the 90-day SOI was +2.5, both in ENSO neutral range. The gradual decrease in the 90-day SOI continues to indicate the formation of an El-Niño event.

Difference from average sea surface temperature observations 1 May to 7 May 2023

30-day Southern Oscillation Index (SOI) values ending 8 May 2023

The El Niño WATCH issued by the Bureau of Meteorology continues. This indicates that there is around a 50% chance that an El Niño may develop later in 2023. El Niño WATCH is not a guarantee that El Niño will occur, but it is an indication that some of the typical precursors are currently observed. A significant amount of warmer than average water temperature exists in the western and central tropical Pacific sub-surface, and warmer than average SSTs have emerged in parts of the eastern tropical Pacific in recent weeks. All but one international climate model surveyed by the Australian Bureau of Meteorology suggest sea-surface temperatures in the tropical Pacific will exceed El Niño thresholds in July.

International climate model outlooks for the ENSO in NINO 3.4 region

The Indian Ocean Dipole (IOD) is currently neutral. A negative phase typically sees above average winter-spring rainfall in Australia, while a positive phase brings drier than average seasons. All international climate models surveyed by the Bureau of Meteorology suggest a positive IOD event may develop in June. A positive IOD can supress winter and spring rainfall over much of central and south-eastern Australia, potentially exacerbating the drying effect of El Niño.

International climate model outlook for the Indian Ocean Dipole

The Southern Annular Mode (SAM) index is currently positive and is expected to return to neutral towards the end of May. SAM typically has a weaker influence on Australian rainfall during autumn, but as we approach winter, positive SAM often has a drying influence for parts of south-west and south-east Australia.

Southern Annular Mode (SAM) daily index

These climate outlooks are generated by ACCESS–S (Australian Community Climate Earth-System Simulator–Seasonal). ACCESS–S is the Bureau of Meteorology's dynamic (physics-based) weather and climate model used for monthly, seasonal, and longer-lead climate outlooks. For further information, go to http://www.bom.gov.au/climate/ahead/about/.

The Bureau of Meteorology’s latest rainfall outlook for June 2023 indicates drier than average conditions are expected across much of Australia.

The ACCESS-S climate model suggests that there is a 75% chance of rainfall totals between 10 and 50 millimetres across eastern New South Wales, scattered areas of coastal Queensland, much of Victoria and Tasmania, southern South Australia, and the southwest of Western Australia. Rainfall totals in excess of 100 millimetres are expected along coastal southwest Western Australia and western Tasmania.

There is a 75% chance of rainfall totals of between 10 and 50 millimetres across most southern cropping regions. The exceptions being Queensland, northern New South Wales and parts of northern Victoria and eastern South Australia where June rainfall totals are expected to be below 10 millimetres. Given that many southern Australian winter cropping regions have received enough rainfall to constitute a consolidated autumn break in March and April, these forecast rainfall totals are likely to be sufficient to provide a favourable start to the winter season. Across parts of northern New South Wales and Queensland where soil moisture levels are below average and the expectation of rainfall totals of below 10 millimetres present a significant downside risk for winter crop production.

Rainfall totals that have a 75% chance of occurring in June 2023

The rainfall outlook for June to August 2023 suggests that below median rainfall is likely to very likely (60% to greater than 80% chance) for much of Australia. However, there is close to equal chances of above or below median rainfall for parts of tropical Queensland and the Northern Territory, coastal New South Wales, central and northern Western Australia, as well as in the western Tasmania.

Bureau of Meteorology rainfall outlooks for June to August have greater than 55% past accuracy across most of Australia. Outlook accuracy is greater than 65% across large areas of western and eastern Australia. However, there is low past accuracy for scattered areas of northern Australia.

Chance of exceeding the median rainfall June to August 2023

The outlook for June to August 2023 suggests there is a 75% chance of rainfall totals between 25 and 200 millimetres across central and eastern New South Wales, the southeast and coastal Queensland, southern parts of South Australia and Western Australia, and much of Victoria and Tasmania. Rainfall totals more than 200 millimetres are forecast for alpine regions of Victoria and New South Wales (snowy mountains), part of coastal northeast Queensland, far southwest of Western Australia and western Tasmania.

Across most winter cropping regions there is a 75% chance of receiving between 25 and 100 millimetres, except for northern Queensland where rainfall totals are expected to be below 25 millimetres.

Rainfall totals that have a 75% chance of occurring June to August 2023

The temperature outlook for June to August 2023 indicates that maximum temperatures across the tropical north and central Australia are likely to be close to the 1990-2012 average (-1°C to +1°C) while slightly warmer (up to +2°C) across much of New South Wales, central and southern Western Australia, southern Queensland, northern Victoria, and in parts of South Australia and isolated parts of southern Tasmania. The minimum temperatures across most of Australia are expected to be close to the 1990-2012 average (-1°C to +1°C).

Predicted maximum temperature anomaly for June to August 2023

Predicted minimum temperature anomaly for June to August 2023

Over the 8-days to 18 May 2023, high-pressure systems will keep much of the country dry. Fronts and troughs will bring showers to southern parts of Australia. Moist onshore winds will bring showers along the coasts of New South Wales and Queensland.

Across Australian cropping regions, rainfall totals of up to 15 millimetres are expected for southeast Queensland. Little to no rainfall is expected for the remaining cropping regions in the next eight days. Despite the lack of a typical autumn break¬ across some southern growing regions, numerous lower rainfall total (5 to 15 millimetre) events have slowly built up the level of soil moisture, giving growers increased confidence to continue to plant winter crops given above average soil moisture levels in many regions.

Total forecast rainfall for the period 11 May to 18 May 2023