Climate and Sustainability
Autumn 2026: Cyclonic activity in the north, quieter season elsewhere
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The Australian Actuaries Climate Index (AACI) recorded a positive value for the 43rd consecutive time in the Autumn of 2026, indicating that the frequency of extreme weather across Australia remains above the 1981–2010 reference period average.
The composite index, which combines high temperature, rainfall, wind and sea level, showed positive values across almost all regions. These were primarily driven by elevated sea levels and extreme wind in cyclone affected regions, warmer temperatures along the east coast, and elevated rainfall in select regions.
Despite the ongoing streak of positive composite index values for Australia as a whole, many regions experienced fairly benign conditions between March and May, recording lower composite index values than the previous season for that region. Key exceptions were the Monsoonal Northeast and surrounds for sea level and wind, which were affected by Cyclone Narelle, and Rangelands South Australia for rainfall.
The extreme sea level index remained elevated across Australia throughout Autumn. The Monsoonal Northeast region recorded a new all-time high for the extreme sea level index, surpassing the previous record set in summer 2025/26 . Surrounding regions also saw elevated sea level index results, with the Queensland Wet Tropics region observing its third-highest value on record.
These heightened index values are a potential result of severe Tropical Cyclone Narelle. This made landfall as a Category 4 System on the North Queensland coast before making its way across northern Australia and eventually into Western Australia. Narelle became only the second system on record to make landfall as a severe tropical cyclone (Category 3 or stronger) across all three of Queensland, Northern Territory and Western Australia since records began in 1980-81 [1] .
Tropical Cyclones can elevate sea levels through a combination of low atmospheric pressure, strong surface winds and storm surge [2] . Beyond cyclonic activity, persistently warm sea surface temperatures may also have contributed to the high sea levels seen this season. Sea surface temperatures remain above average around most of Australia, and global sea surface temperatures have been described as exceptionally warm [3] . Warmer water expands in volume through thermal expansion, directly contributing to elevated sea levels.
This is reflected in the recent transition from La Niña into an El Niño phase of the El Niño-Southern Oscillation (ENSO) weather system [4] . El Niño phases are characterised by warmer than average ocean temperatures in the central and eastern Pacific, which influence both sea surface temperatures and broader climate patterns across the region.
Gale force level winds are a defining characteristic of tropical cyclones, with the most powerful winds appearing near the centre of the system. Narelle generated significant wind gusts across northern Queensland, the top of the Northern Territory and throughout parts of Western Australia, driving several of the positive extreme wind index values recorded this season.
The extreme rainfall index remained positive across most of Australia in Autumn 2026. However, several regions also demonstrated negative index values, highlighting the regional variability of rainfall extremes.
Southern Australian regions recorded positive index values, with Rangelands South Australia observing its highest index value in the past three years. Several rainfall records were broken across the state in May, including at Gluepot Reserve in the Mallee district, which observed a total of 205.4mm of rain across the season [5] .
Both the extreme high and extreme low temperature indices recorded very small positive index values for Australia as a whole.
The extreme high temperature index remained elevated in parts of New South Wales, Victoria and Tasmania, consistent with the Bureau of Meteorology’s observation that the three states had all recorded a top-10 warmest autumn on record. However, these were offset by negative index values in all other regions.
On 16 June, the Bureau of Meteorology officially declared an El Niño event underway [6] . Forecasts indicate that this will be a strong to very strong event, with the extent of warming in the central tropical Pacific potentially reaching a peak not seen since 1950 [7] . This event is expected to persist until at least the end of the year.
Meanwhile, the Southern Annular Mode (SAM) is currently positive, which is associated with stronger westerly winds and wetter conditions in southern Australia. A positive SAM can also push cold fronts further south, towards Antarctica, contributing to milder temperatures. This pattern has contributed to an unusually warm and wet start to winter 2026 [8] . However, the SAM is forecast to return to neutral in coming weeks, removing this wetter influence and allowing the drying effect of the strengthening El Niño to dominate [9] .
Combined, these drivers contribute to a long-range forecast for July to September 2026 of below-average rainfall in southern and eastern Australia and warmer-than-average daytime and overnight temperatures [10] .
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 [11] .
Alongside the North American Actuaries Climate Index [12] , 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 Columbia, Singapore and the Caribbean, have or are in the process of launching similar indices.
[1] Bureau of Meteorology. (2026, March 24). Severe Tropical Cyclone Narelle's journey across northern Australia. http://www.bom.gov.au/news-and-media/severe-tropical-cyclone-narelles-journey-across-northern-australia
[2] Bureau of Meteorology. (2017, May 24). Tropical cyclones at sea: The ocean below the storm [Blog post]. http://media.bom.gov.au/social/blog/1381/tropical-cyclones-at-sea-the-ocean-below-the-storm/
[3] Copernicus Climate Change Service. (2026, May 8). Copernicus: Second-highest sea surface temperatures recorded during third-warmest April globally. https://climate.copernicus.eu/copernicus-second-highest-sea-surface-temperatures-recorded-during-third-warmest-april-globally
[4] 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
[5] Australian Broadcasting Corporation. (2026, June 9). Record rain brings crop improvements for SA farmers. ABC News. https://www.abc.net.au/news/2026-06-09/record-rain-sa-farmers-crop-improvements/106771550
[6] Bureau of Meteorology. (n.d.). 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
[7] Bureau of Meteorology. (n.d.). ENSO Wrap-Up: Niño 3.4 index. http://www.bom.gov.au/climate/enso/?ninoIndex=nino3.4&index=rnino34&period=weekly
[8] 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
[9] Bureau of Meteorology. (n.d.). ENSO Wrap-Up: Southern Ocean. http://www.bom.gov.au/climate/enso/?ninoIndex=nino3.4&index=rnino34&period=weekly#tabs=Southern-Ocean
[10] Bureau of Meteorology. (2026, March 12). Seasonal climate outlook, issued 12 March 2026 [Archived outlook]. http://www.bom.gov.au/climate/ahead/outlooks/archive/20260312-outlook.shtml
[11] Royal Commission into National Natural Disaster Arrangements. (n.d.). Exhibit 1-006: Australian Actuaries Climate Index -- some comments on extremes [Exhibit]. 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/
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivatives CC BY-NC-ND Version 4.0.
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