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Winter 2026: Record warmth and concentrated rainfall
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The Australian Actuaries Climate Index (AACI) recorded its 44th consecutive positive value in the winter of 2026, indicating that the frequency of extreme weather across Australia continues to remain above the 1981–2010 reference period average.
The composite index, which combines the high temperature, rainfall, wind and sea level indices showed positive values, primarily concentrated in southern parts of Australia. These were driven by warmer temperatures and elevated rainfall in these regions.
Unusually warm nights and elevated extreme high temperatures observed throughout Australia
Winter 2026 was characterised as being one of the warmest in recent history, with the Bureau of Meteorology (BOM) noting it as the equal third-highest area-average mean temperature ever on record [1] .
The extreme low temperature index recorded its highest ever value, with positive values observed across all regions.
Notably, the Coastal New South Wales and Queensland Temperate Coast regions which encompass Sydney and Brisbane respectively saw their highest-ever extreme low temperature index values. This is largely consistent with the Bureau of Meteorology’s observation that mean minimum temperatures were above to very above average across most of Australia.
Heightened and more extreme minimum temperatures can pose serious risks to society. Milder winter lows may result in a greater prevalence of pests and vector-borne diseases. There are also physical risks, as heightened minimum temperatures can prevent recovery from heat stress at night which can result in increased mortality [2] .
The extreme high temperature index showed elevated index values across most regions, with the exception of northern Australia.
Tasmania recorded its greatest ever extreme high temperature index value, aligning with the BOM’s note that Tasmania observed its highest mean maximum temperature for winter ever. Similar trends were observed in New South Wales and Victoria, though neither state set a new record.
Although increases in the mean maximum temperature were also observed by the BOM for Queensland and large parts of the Northern Territory [3] , the index returned negative values. This illustrates the differences between extreme temperatures and high averages (means). Changes in each may have significant impacts on society in various ways, as noted in previous releases .
There are several key drivers of these unusually warm days and nights in winter 2026. The now well-established El Niño event reduces cloud cover, resulting in heightened daytime temperatures. Elevated sea-surface temperatures can result in more evaporation. This increases moisture in the atmosphere and traps more heat, preventing temperatures from lowering more at night [4] .
Rainfall extremes concentrated around South Australia and Victoria
The extreme rainfall index recorded a positive index value for Australia in winter 2026. Despite this, more than half of the regions observed negative index values, reflecting the localised nature of extreme rainfall events and the significant regional variability that occurs across Australia.
Regions across southern Australia have recorded positive index values. Wider Adelaide observed its highest ever index value while Rangelands South Australia saw its highest index value in the past 10 years, largely surpassing the three-year high observed in Autumn 2026 . These heightened index values were due to South Australia experiencing its wettest winter since 1978 [5] , with Adelaide receiving 294.4mm of rain alone across the season [6] .
Key contributors were several powerful cold fronts [7] that appeared across winter along with a positive Southern Annular Mode (SAM) in June, which is associated with wetter conditions in southern parts of Australia [8] .
Implications for the upcoming bushfire season
In areas that received sustained above-average rainfall, the relatively warm and wet winter may have supported additional vegetation growth and increased potential fuel loads. Whether this translates into greater bushfire risk will depend on subsequent spring and summer conditions: prolonged warm, dry and windy weather could rapidly cure this vegetation and make it more flammable, enabling a severe bushfire season.
High sea levels remain the norm
The Sea Level index continues to remain elevated across Australia throughout winter, with all regions observing positive index values.
Regions along the south-east coast of Australia recorded greater index values than observed in autumn. Sea surface temperature analysis showed that waters were especially warm along the New South Wales and Tasmanian coasts throughout June to August, with a peak of around 3 - 4 °C above the average [9] . Warmer sea surface temperatures contribute to heightened sea levels through thermal expansion.
In June 2026, the Bureau of Meteorology officially declared an El Niño event underway. Since then, it is now firmly established, with several indices reflecting signs consistent with a strong El Niño [10] . The BOM expects further intensification throughout spring, with it peaking in late spring / summer as a “very strong event”. The strong El Niño is already affecting global weather, as is evidenced by hurricane seasons in the Northern Hemisphere. There has been an extremely active eastern and central North Pacific season, an unusual number of storms in the Hawaiian region, and one of the least active North Atlantic seasons on record.
Sea surface temperatures are forecast to continue warming in the next few months. These can enhance atmospheric moisture, providing fuel for stronger storms and rain systems, as well as contribute to heightened temperatures by trapping more heat.
These drivers result in a long-range forecast for October to December of above-average rainfall in west and central Australia, below-average rainfall in south-eastern Australia and warmer-than-average daytime and overnight temperatures. The SAM is currently negative and is expected to shift into a neutral state in the coming weeks. The Indian Ocean Dipole (IOD) was neutral at the time of writing, although forecasts indicated that a positive IOD could develop during spring. A positive IOD typically reduces rainfall across central and southern Australia and, if it develops alongside El Niño, could reinforce the drier outlook for south-eastern Australia [11] .
The Index measures the frequency of extreme weather conditions and sea levels across Australia and how these vary over time. Components cover extreme high and low temperatures, extreme rainfall, consecutive dry days (as an indicator of drought), extreme wind and sea level. The Index was first launched in November 2018 by the Actuaries Institute and version 2.0, which includes enhancements not available at the time of the original Index, was released in 2025. It is updated four times a year by Finity Consulting for the Actuaries Institute.
Unlike many other measures, the AACI focuses on changes in the extremes. This is a more relevant metric for the insurance industry (and others) than averages, as it correlates more closely with damage. This is done by measuring how often we observe the current quarter’s observations exceeding the 99th percentile of the corresponding observations in the reference period of 1981-2010. More details and full results can be found on the website .
The purpose of the AACI is to provide a publicly available and objective measure of extreme weather conditions and sea level and is one way in which the actuarial profession can contribute to the assessment of climate risk. The AACI has been referenced extensively in the media and other reports [12] .
Alongside the North American Actuaries Climate Index [13] , it is one of two climate indices which have been produced globally for several years on behalf of actuarial associations. Several other actuarial associations, including Colombia, Singapore and the Caribbean, have or are in the process of launching similar indices.
[1] Bureau of Meteorology. (2026, September 1). Australia in winter 2026. http://www.bom.gov.au/clim_data/IDCKGC2AR0/202608.summary.shtml
[2] Kenney, W. L., Craighead, D. H., & Alexander, L. M. (2014). Heat waves, aging, and human cardiovascular health. Medicine & Science in Sports & Exercise, 46(10), 1891–1899. https://pmc.ncbi.nlm.nih.gov/articles/PMC4155032/
[3] Sharwood, A. (2026, September). Why the 2026 winter was the warmest on record across large parts of Australia. Weatherzone. https://www.weatherzone.com/au/news/why-the-2026-winter-was-the-warmest-on-record-across-large-parts-of-australia/1891536
[4] Bureau of Meteorology. (2026, September 1). Australia in winter 2026. http://www.bom.gov.au/clim_data/IDCKGC2AR0/202608.summary.shtml
[5] Australian Broadcasting Corporation. (2026, June 16). Bureau of Meteorology declares El Niño weather event. ABC News. https://www.abc.net.au/news/2026-06-16/nsw-bureau-of-meterology-declares-el-nino-weather/106776598
[6] Australian Broadcasting Corporation. (2026, August 8). Flooding rain and gales ahead for southern Australia in coming days. ABC News. https://www.abc.net.au/news/2026-08-08/australian-weather-flooding-rain-ahead-for-southern-states/107009816
[7] Australian Broadcasting Corporation. (2026, June 27). Heavy rain forecast for eastern Australia as El Niño weather pattern develops. ABC News. https://www.abc.net.au/news/2026-06-27/heavy-rain-australia-east-as-el-nino-weather/106848044
[8] Bureau of Meteorology. (n.d.). Climate outlooks. http://www.bom.gov.au/climate/ahead/outlooks/
[9] Bureau of Meteorology. (2026, September 17). El Niño: What it means for Australia's climate. http://www.bom.gov.au/news-and-media/el-nino-what-it-means-for-australias-climate
[10] Bureau of Meteorology. (2026, September 15). ENSO Wrap-Up: Overview. http://www.bom.gov.au/climate/enso/?ninoIndex=nino3.4&index=rnino34&period=weekly#tabs=Overview
[11] Royal Commission into National Natural Disaster Arrangements. (n.d.). Exhibit 1-006: Australian Actuaries Climate Index — some comments on extremes [Exhibit]. https://webarchive.nla.gov.au/awa/20211005174723/https://naturaldisaster.royalcommission.gov.au/publications/exhibit-1-006003-shp5010010001-australian-actuaries-climate-index-some-comments-extremes
[12] Actuaries Climate Index. (n.d.). Home. https://actuariesclimateindex.org/home/
The views expressed in this article are those of the author(s) or working group named below, and do not necessarily reflect the views of the Actuaries Institute. This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivatives CC BY-NC-ND Version 4.0.
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