Australian tropical cyclone season long-range forecast
About the long-range forecasts
The tropical cyclone season long-range forecast uses the statistical relationships between historical tropical cyclone numbers and two indicators: the Southern Oscillation Index (SOI) and the Niño3.4 sea surface temperature (SST) anomaly (relative to the 1991–2020 average). These two indicators provide a measure of the atmospheric and oceanic state, respectively, of El Niño-Southern Oscillation (ENSO).
The July, August and September SOI and NINO3.4 anomaly values are used in making the Australian Tropical Cyclone Outlook.
Interpreting the long-range forecast
The statistical long-range forecast generates a percentage chance that the upcoming season will have more tropical cyclones than the long-term average. For example, a 40% chance of having more than average tropical cyclones means that for every ten years with similar ENSO patterns to those currently observed, four years would be expected to have an above average number. The percentage chance is converted into a categorical forecast whether each region is expected to have an above average, average, or below average number of tropical cyclones.
The long-term average, since 1969–70, number of tropical cyclones per season in the Australian region is 11, with 4 typically making landfall. In the South Pacific region, the long-term average is 9 tropical cyclones per season.
In recent decades, in a globally warmer climate, the total number of tropical cyclones that have formed in the Australian region has decreased, to an average of 9 per season since 2000–01. In a globally warmer climate, it is generally more difficult for tropical cyclones to form due to less favourable atmospheric conditions. However, due to increased energy provided by warmer oceans, tropical cyclones that do form are likely to be more intense and produce more rainfall.
During El Niño events, there are typically fewer tropical cyclones than average, while more tend to occur during La Niña events.
Australian region long-range forecast accuracy
Historically, over the entire Australian Region, this statistical relationship has had high accuracy, i.e. has skilfully predicted total tropical cyclone activity. However, across the sub-regions this relationship, and thus forecast skill, can vary. The North-western sub-region has moderate to high skill, the Western region has moderate skill, and Eastern and Northern regions both have low skill.
The statistical relationship between historical tropical cyclones numbers and climate indicators used by the long-range forecast does not explicitly include global warming.
Australian tropical cyclone long-range forecast region bounds
| Region | Top | Bottom | Left | Right |
|---|---|---|---|---|
| Australian region | 5° S | 40° S | 90° E | 160° E |
| Western region | 5° S | 40° S | 90° E | 125° E |
| NW sub-region | 5° S | 25° S | 105° E | 130° E |
| Northern region | 5° S | 40° S | 125° E | 142.5° E |
| Eastern region | 5° S | 40° S | 142.5° E | 160° E |
Current information
- Tropical Climate Update
- Tropical (MJO) monitoring
- Southern Oscillation Index (SOI)
- SST indices
- SST analysis maps
- SST outlooks
- Latest Northern wet season summary
- Tropical cyclone climatology maps
Tropical cyclone knowledge centre
Definitions
South Pacific
References
Research documents
Model: Kuleshov, Y., L. Qi, R. Fawcett and D. Jones, 2008: Improving preparedness to natural hazards: Tropical cyclone prediction for the Southern Hemisphere, in Advances in Geosciences, 12 Ocean Science, (Ed. Gan, J.), World Scientific Publishing, Singapore, 127-143.
Data: Kuleshov, Y., R. Fawcett, L. Qi, B. Trewin, D. Jones, J. McBride and H. Ramsay, 2010: Trends in tropical cyclones in the South Indian Ocean and the South Pacific Ocean, Journal of Geophysical Research 115, D01101, doi:10.1029/2009JD012372.
Tropical cyclone numbers likely to be close to average for Australia in 2024–25
- The 2024–25 Australian tropical cyclone season is expected to be like the long-term average, in which 11 tropical cyclones form in the Australian region, 4 of which cross the Australian coast.
- The likelihood of severe (strong) tropical cyclones is higher than average, because of the warmer than average ocean temperatures forecast for the Australian region in the coming months.
- Under the prevailing neutral climatic conditions, the first tropical cyclone to cross the Australian coast typically occurs in late December.
- Tropical cyclone formation is rarely evenly spread throughout the season; quiet periods are often followed by bursts of activity.
- Cyclones are not the only weather hazard in the Australian tropics. Tropical lows can also cause damaging winds, widespread rainfall and dangerous flooding.
- Storm surge, including from cyclones that don't make landfall, is a major hazard to coastal communities. These impacts can extend beyond the tropics into southern parts of Australia.
- Due to rising sea levels, the risk of storm surge from tropical cyclones is likely to continue to increase.
Seasonal forecast
Our long-range forecast for the seasonal risk is based on statistical modelling, which includes conditions in the oceans and atmosphere over the preceding July to September period, and information based on what has happened in all seasons since 1969–70.
The tropical cyclone season typically runs from 1 November to 30 April, although tropical cyclones can, and do, form outside of these dates. All tropical cyclones that are active between 1 July and 30 June count toward the season's total. The broader Australian region covers the area south of the equator, between 90°E and 160°E, and includes Australian, Papua New Guinea, and Indonesian areas of responsibility.
Product code: IDCKAUTCSO
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