as seas off Australia run up to 3°C hotter
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Adelaide reached 34.4°C at 1.36pm on a September afternoon, its second-hottest September day on record.
More than a dozen South Australian sites broke September heat records under hot, dry northerly winds.
Bureau of Meteorology senior meteorologist Dean Narramore said it "felt more like January than September".[3]
El Niño, the warm phase of the El Niño–Southern Oscillation (ENSO), heats the central and eastern tropical Pacific Ocean.
It now sits at near-record levels as seas off Australia's west, south and south-east run up to 3°C above average.
A positive Indian Ocean Dipole, a temperature contrast across that ocean basin, is likely to develop.[1]
The weekly relative Niño3.4 index gauges sea surface temperature (SST) warmth in the central equatorial Pacific. It reached +2.81°C in the week ending 11 October 2026, a record for the Bureau's weekly SST data.
The weekly series starts in 2008, and the previous high was +2.78°C in the week ending 22 November 2015.[1]
Sustained monthly relative Niño3 or Niño3.4 values above +0.8°C signal El Niño to Bureau climatologists. That threshold sits roughly one standard deviation from the long-term mean. The latest weekly reading exceeds it by more than 2°C.[1]
All models, including the Bureau's, forecast the tropical Pacific warmth to peak around November or December. Most models indicate a monthly peak above +3.0°C, higher than the warmest observed since reliable records began in 1950. The Bureau expects the event to persist into autumn 2027.[1]
Marine heatwaves are spells of prolonged, extreme ocean warmth. The World Meteorological Organization (WMO) ranked 2025 coverage the most extensive on record for a non-El Niño year. Record upper-ocean heat content in 2025 also covered waters south of Australia and the southern Tasman Sea.[4]
Trade winds normally blow steadily from east to west across the tropical Pacific. This El Niño has weakened or reversed them across the western to central basin. Cloudiness has increased across the central to eastern Pacific and dropped over the Maritime Continent of Southeast Asia.[1]
The 30-day Southern Oscillation Index (SOI) read −20.2 on 11 October 2026. The El Niño threshold sits at −7, and the index compares air pressure between Tahiti and Darwin. Short-term weather dominates single-day and weekly values, so the Bureau issues 30-day and monthly figures instead.[1]
For October to December, the Bureau's outlook favours drier than average conditions in parts of the south-east and north-east. Odds also favour warmer than usual days and nights. Background warming from climate change makes above-average temperatures increasingly likely.[5]
Australia's September mean temperature ran 2.71°C above the 1961–1990 average, the second-highest on record. Minimum temperatures hit a national record 2.52°C above average, while rainfall fell 17 per cent below average. Western Australia posted its highest September minimum on record, at 3.19°C above average.[6]
The weekly Indian Ocean Dipole (IOD) index reached +0.88°C in the week ending 11 October 2026. That marks the fifth consecutive week above the +0.4°C positive threshold. Sustained values must confirm an event, so the IOD remains neutral for now.[1]
Climatologists calculate the IOD from the difference between SSTs in the western and eastern tropical Indian Ocean. A positive phase brings cooler than average water in the east and warmer than average water in the west. Australian climatologists treat sustained values above +0.4°C as typical of a positive event.[1]
Before the satellite era, ships passing through each region supplied most ocean temperature observations. Those observations arrived too rarely to build a reliable weekly dataset. Event identification from early records carries limited accuracy, particularly for the IOD before 1960.[1]
A strong Pacific signal carries uncertain local consequences because ENSO is one influence among many. Model guidance also shows uncertainty in the strength and duration of the expected positive IOD. The Bureau's long-range forecast offers the best guidance on likely rainfall and temperature patterns.[1]
SSTs reached up to 3°C above average off Australia's west, south and south-east in the week to 11 October. The Bureau forecasts further warming across most of the Australian region, particularly in the west and the Coral Sea. Warmer water carries more atmospheric moisture and energy, which can fuel storms and high-intensity rainfall.[1]
September 2026 ranked as the warmest September on record for ocean surface temperatures between 60°S and 60°N. It ran 1.02°C above the 1961–1990 average. September also placed third among all months since 1900, behind August 2026 and August 2023.[1]
Kelp forests, underwater stands of large brown seaweed, anchor southern Australia's temperate reefs. CSIRO reports that warm water, low nutrients and sea urchins have cut Tasmania's giant kelp forests by 95 per cent. The East Australian Current has pushed further south, delivering nutrient-poor water and invading urchins.[7]
Tasmanian Aboriginal divers collect every abalone by hand through the Land and Sea Aboriginal Corporation Tasmania. Divers skip the summer spawning season even when export markets want supply. Director Daniel Kelleher says abalone rely on cool, nutrient-rich water and giant kelp has nearly vanished from the east coast.[8]
The Bureau replaced Traditional Niño indices with Relative Niño indices in September 2025. Relative indices subtract the tropical mean warming, isolating the local signal of ENSO from global warming. The Niño3.4 region spans 5°N to 5°S and 170°W to 120°W.[1]
Rain-bearing westerly winds shift north and south across the Southern Ocean, and the Southern Annular Mode (SAM) tracks that movement. A positive SAM means a southward shift from the usual seasonal position, while a negative SAM means a northward shift. The Bureau expects the index to return to neutral within days after reading positive on 10 October.[1]
Daily gap-free SST analyses draw on drifting buoys, moored buoys, ships and infrared radiometers aboard polar-orbiting satellites. The US agency NOAA and the European Space Agency operate those satellites, and Japan's JAXA adds microwave sensors. The analysis estimates temperature near 0.2 metres depth, similar to readings through the top 10 metres under well-mixed conditions.[1]
Five states manage Australia's kelp forests independently, a patchwork across more than 8,000 kilometres of the Great Southern Reef. The Environment Protection and Biodiversity Conservation Act 1999 lists giant kelp as Endangered. Tasmania has still lost about 95 per cent, while Western Australia lost 96,300 hectares in 2011.[2]
The data converge on a clear picture. El Niño has reached record weekly strength, atmospheric signals confirm it, and a positive Indian Ocean Dipole is forming. Summer arrives with the Pacific still warming toward its peak.
Warm seas off the west, south and south-east coasts extend the risk beyond the Pacific. Kelp forests and the Aboriginal enterprises that depend on cool water stand on that frontline.
Accountability gaps remain visible. Five state systems manage kelp forests, yet Tasmania has lost about 95 per cent of its listed giant kelp.
The coming peak tests whether governments coordinate monitoring and protection across state boundaries.
1. Bureau of Meteorology: Southern hemisphere monitoring (update for the week ending 11 October 2026). Primary source for the Niño3.4, Southern Oscillation Index, Indian Ocean Dipole, Southern Annular Mode, sea surface temperature and methodology figures.
2. NESP Marine and Coastal Hub: Quantifying the ecosystem services of the Great Southern Reef. Documents state-by-state kelp management, the Endangered listing of giant kelp and the scale of recorded kelp losses.
3. ABC News: Records fall as September temperatures soar in South Australia. Reports the September heat records and Bureau of Meteorology commentary across South Australia.
4. World Meteorological Organization: Ocean warming, marine heatwaves and sea-level rise pose increasing risk in South-West Pacific region. Supplies 2025 marine heatwave coverage and ocean heat content findings for the region.
5. RenewEconomy: El Niño nears record levels as ocean conditions tilt in unfavourable direction for eastern Australia. Summarises the Bureau's October to December rainfall and temperature odds.
6. Bureau of Meteorology: Australia in September 2026. Provides national September temperature and rainfall anomalies and the Western Australian minimum temperature record.
7. CSIRO: An ocean forest in danger. Explains the 95 per cent decline of Tasmanian giant kelp and its links to warming, low nutrients and urchins.
8. SBS Food: On Sea Country, how Tasmanian Aboriginal people have cared for abalone for millennia. Records Tasmanian Aboriginal abalone harvesting practice and concern about kelp loss on the east coast.
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