Weekly update - 27 May 2021

During the week ending 26  May 2021, blocking high pressure systems resulted in little rainfall being recorded across much of Australia. However, low pressure troughs and cold fronts generated moderate rainfall across isolated parts of western, southern and eastern Australia.

Rainfall totals of between 5 and 50 millimetres were recorded across parts of southern New South Wales, north-eastern Queensland, southern and central Victoria, southern South Australia, south-western Western Australia, and Tasmania. Rainfall totals in excess of 50 millimetres were recorded across isolated parts of north-eastern Queensland, eastern Victoria, south-western Western Australia and north-western Tasmania.

In cropping regions, rainfall totals of between 5 and 25 millimetres was recorded across parts of southern New South Wales and much of Victoria, South Australia and Western Australia. Rainfall totals in excess of 25 millimetres was recorded across isolated parts of south-eastern Victoria, western South Australia and southern Western Australian cropping regions. Little to no rainfall was recorded across cropping regions in northern New South Wales and Queensland during the week ending 26 May 2021.

These falls across southern cropping regions will benefit the establishment of dry sown winter crops and encourage addition planting activity. Further rainfall will be needed to support crop growth and benefit yields, particularly in South Australia and parts of Victoria where soil moisture is low.

Rainfall for the week ending 26 May 2021

©Commonwealth of Australia 2021, Australian Bureau of Meteorology - Issued: 26/05/2021
Note: The rainfall analyses and associated maps utilise data contained in the Bureau of Meteorology climate database, the Australian Data Archive for Meteorology (ADAM). The analyses are initially produced automatically from real-time data with limited quality control. They are intended to provide a general overview of rainfall across Australia as quickly as possible after the observations are received. For further information go to http://www.bom.gov.au/climate/rainfall/

Throughout winter the climate drivers with the largest potential impact on Australia’s climate patterns are the El Niño–Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM). These climate drivers will likely influence the outlook for Australia’s winter cropping season.

Analysis of oceanic and atmospheric indicators suggest that ENSO conditions remain neutral, reducing its influence on Australia’s climate patterns. Analysis of sea surface temperatures in tropical Indian Ocean indicate that the IOD is also currently neutral.

A neutral ENSO and IOD means these climate drivers are unlikely to have much influence over Australia’s climate over the short-term. If neutral ENSO and neutral IOD conditions persist into winter, the SAM will likely be the main influence on winter rainfall.

The SAM is currently negative and is expected to remain negative for the next week then increase towards neutral over the following week. At this time of year negative SAM can enhance rainfall over south-west Western Australia and south-eastern Australia, and reduce rainfall for western parts of the coastline of the Great Australian Bight, New South Wales, and southern Queensland.

Over the past weeks, sea surface temperature anomalies have been close to average across the tropical Pacific Ocean. This return to long-term average sea surface temperatures is associated with the return to a neutral ENSO. As of 25 May 2021, all of the international climate models surveyed predict sea surface temperatures in the tropical Pacific to remain neutral until at least October.

Sea surface temperatures near Western Australia, the south and east coast of Australia and Indonesia remain above average. The warm temperature anomalies in the southern and eastern Indian Ocean have remained largely unchanged over the past couple of weeks, while warm anomalies in the north-eastern Indian Ocean have strengthened. Warm anomalies in the eastern Indian Ocean and the ocean surrounding Australia are associated with increased rainfall across parts of Australia.

Difference from average sea surface temperature observations 17 May to 23 May 2021

International climate model outlooks for the NINO 3.4 region in October 2021

©Commonwealth of Australia 2021, Australian Bureau of Meteorology - Issued: 25/05/2021

Trade wind strength across the tropical Pacific has remained close to average over the past fortnight. Cloudiness near the Date Line has also remained close to average over the past fortnight. Average trade wind strength and cloudiness near the Date Line are associated with neutral ENSO conditions. The Southern Oscillation Index (SOI) provides an atmospheric measure of the development and intensity of the ENSO by assessing air pressure differences between Tahiti and Darwin. The 30-day SOI for the period ending 23 May was +5.5. For the period ending 23 May, the 90-day SOI value was +1.5. The 30-day and 90-day SOI have stabilised below the La Niña threshold value of +7. Overall, the SOI values indicate a continuation of neutral conditions.

30-day Southern Oscillation Index (SOI) values ending 23 May 2021

As at 23 May, the Indian Ocean Dipole (IOD) weekly value was -0.46°C, which is weakly negative. For an IOD event to be declared, negative IOD values must be sustained for 8 consecutive weeks. The international climate models surveyed by the Bureau of Meteorology have mixed expectations for the months ahead. One of the five models predict a negative IOD in June (below -0.4°C), while four anticipate the IOD remaining neutral. By September, a different model predicts a negative IOD, while the remaining four anticipate neutral IOD conditions. A positive IOD is associated with lower rainfall and above average temperatures across southern Australia during winter and spring. A negative IOD is associated with above average winter and spring rainfall across southern Australia, as well as the far north. It is also associated with an early northern rainfall onset.

Monthly sea surface temperature anomalies for IOD region

The Southern Annular Mode (SAM) is currently negative and expected to remain negative over the coming week, before returning toward neutral. The SAM refers to the north-south shift of the band of rain-bearing westerly winds and weather systems in the Southern Ocean compared to the usual position. A negative SAM in winter is associated with increased rainfall for northern New South Wales, southern Queensland and southern parts of South Australia and Western Australia. It is also associated with decreased rainfall for much of Victoria, the west of Western Australia and Tasmania.

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 dynamical (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 indicated wetter than average conditions are more likely for parts of north-western, central and eastern Australia during June. It should be noted that May marked the beginning of the northern Australian dry season. This means tropical northern Australia typically has very low rainfall totals at this time of year, and only a small amount of rainfall is needed to exceed the median. In contrast, the wetter than average conditions expected in parts of south-eastern Australia are likely influence the outlook for Australia’s winter cropping season.

The outlook for June 2021 indicates that there is a 75% chance of rainfall totals between 10 and 100 millimetres across parts of eastern, south-western and far southern Australia. Rainfall totals in excess of 100 millimetres are expected across parts of Tasmania and isolated parts of south-eastern and south-western Australia.

Across cropping regions there is a 75% chance of rainfall totals of between 5 and 10 millimetres in parts of central Queensland. There is a 75% chance of rainfall totals between 10 and 50 millimetres for New South Wales, southern Queensland, Victoria, South Australia and Western Australia.

Rainfall totals that have a 75% chance of occurring June 2021

©Commonwealth of Australia 2021, Australian Bureau of Meteorology - Issued: 20/05/2021

The ACCESS-S climate model suggests there is a 50% chance of recording close to average June rainfall totals across much of Australia, including most cropping regions in New South Wales, central and southern Queensland, Victoria, South Australia and Western Australia. An early autumn break has occurred for much of the New South Wales, southern areas of Queensland, Western Australian and Tasmanian cropping regions. Based on the 50% chance scenario those cropping regions in parts of western Victoria and South Australia that have yet to record an autumn break are forecast to receive between 25 to 50 millimetres of rainfall to support the germination and establishment of winter crops. If realised these forecast rainfall totals for June will provide sufficient moisture for planting of winter crops across most cropping regions.

The rainfall outlook for June to August 2021 suggests there is a greater than 60% chance of above average rainfall across parts of north-western New South Wales, western Queensland, South Australia, eastern Western Australia and much of the Northern Territory. There is a less than 40% chance of exceeding median rainfall across parts of northern Queensland and the west of Western Australia (Bureau of Meteorology ‘National Climate Outlook’, 20 May 2021).

Bureau of Meteorology rainfall outlooks for June to August have greater than 55% past accuracy across most of central and southern Australia. Outlook accuracy is greater than 65% across parts of northern New South Wales, southern Queensland, the south of the Northern Territory and much of Western Australia. In contrast, there is low past accuracy for parts of western and south-eastern New South Wales, northern Queensland, eastern Victoria, south-eastern South Australia, the north of Western Australia and the north of the Northern Territory. This indicates that for this time of the year the outlook model performs no better than random chance in these areas.

Chance of exceeding the median rainfall June to August 2021

©Commonwealth of Australia 2021, Australian Bureau of Meteorology - Issued: 20/05/2021

The outlook for June to August suggests there is a 75% chance of rainfall totals between 50 and 200 millimetres across much of New South Wales and Victoria, and parts of far eastern Queensland, the south of Southern Australia, the southwest of Western Australia and eastern Tasmania. Rainfall totals in excess of 300 millimetres are likely across parts of alpine regions of New South Wales and Victoria, and the far south-western Western Australia and northern and western Tasmania.

Across cropping regions, there is a 75% chance of receiving between 50 and 200 millimetres in New South Wales, Victoria, South Australia and Western Australia. Totals of less than 50 millimetres are expected in Queensland cropping regions.

There is a 50% chance of recording average or close to average June to August rainfall totals across most winter cropping regions. Average to above average soil moisture levels in New South Wales, and parts of Queensland and Western Australia are likely to provide good conditions for the establishment and growth  of winter crops, while the probability of close to average in-season rainfall will assist with yield development in the coming months.

Rainfall totals that have a 75% chance of occurring June to August 2021

©Commonwealth of Australia 2021, Australian Bureau of Meteorology - Issued: 20/05/2021

The temperature outlook for June to August 2021 indicates that day-time and night-time temperatures across most of Australia are likely to be close to the 1990-2012 average (- 1°C to 1°C) (Bureau of Meteorology ‘National Climate Outlook’, 20 May 2021).

Predicted maximum temperature anomaly for June to August 2021

Predicted minimum temperature anomaly for June to August 2021

Low-pressure troughs and cold fronts are likely to bring showers and storms to parts of Western Australia and Tasmania the 8 days to 27 May 2021. High-pressure systems are expected to keep rainfall totals low for the majority of central and south-eastern Australia during the next 8 days.

Rainfall totals of between 5 and 50 millimetres are forecast for isolated parts of north-eastern Queensland, southern Victoria, western Tasmania and much of the west and south of Western Australia.

In Australia’s cropping regions, rainfall totals of between 10 and 50 millimetres are forecast for Western Australia. Rainfall totals of between 5 and 10 millimetres are forecast for isolated parts of western South Australian cropping regions. Little to no rainfall is expected across cropping regions in Queensland, New South Wales, Victoria and remaining cropping regions in South Australia.

The falls across Western Australian cropping regions will likely benefit the establishment and growth of early sown winter crops and allow farmers to finalise planting programs. The dry forecast for the next 8 days across remaining cropping regions will allow for further planting and adequate soil moisture in parts of New South Wales, southern Queensland and southern Victoria will continue to support crop and pasture growth.

Total forecast rainfall (mm) for the period 27 May to 3 June 2021

©Commonwealth of Australia 2021, Australian Bureau of Meteorology - Issued: 27/05/2021
Note: This rainfall forecast is produced from computer models. As the model outputs are not altered by weather forecasters, it is important to check local forecasts and warnings issued by the Bureau of Meteorology.