South Pacific tropical cyclone season 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.
South Pacific countries
This long-range forecast provides general guidance for the South Pacific region. For specific guidance for an individual country, please contact their National Meteorological and Hydrologic Service.
South Pacific region long-range forecast accuracy
The statistical model used for this long-range forecast has a high level of accuracy predicting cyclone numbers in the western region, but a very low level of accuracy for the eastern region.
South Pacific tropical tropical cyclone long-range forecast region bounds
| Region | Top | Bottom | Left | Right |
|---|---|---|---|---|
| Whole South Pacific region | 5° S | 40° S | 142.5° E | 120° W |
| Western region | 5° S | 40° S | 142.5° E | 165° E |
| Eastern region | 5° S | 40° S | 165° E | 120° W |
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.
Average number of tropical cyclones likely in the South Pacific in 2024–25
- The number of tropical cyclones expected during the 2024–25 South Pacific tropical cyclone season (November to April), 6 in the Eastern region and 4 in the Western region, is expected to be close to average.
- The likelihood of severe (strong) tropical cyclones is higher than average, because of the warmer than average ocean temperatures forecast for the South Pacific region in the coming months.
- Due to rising sea levels, the risk of storm surge from tropical cyclones is likely to continue to increase.
- Tropical cyclones can affect Pacific Islands and coastal regions even when they remain well offshore.
- Tropical lows that do not intensify into tropical cyclones, or lows that are the remnants of older tropical cyclones, can still produce damaging winds, widespread rainfall, and dangerous flooding.
The South Pacific 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 average number of tropical cyclones during the season is 4 in the Western region and 6 in the Eastern region.
This forecast is based on the analysis of ENSO oceanic and atmospheric indicators over July to September 2024. The skill of this forecast is limited and the long-term trend towards fewer tropical cyclones can provide better guidance on the expected number of tropical cyclones.
Ocean temperatures are currently cooler that average in parts of the eastern and central equatorial Pacific, close to average in the vicinity of the Date Line, and warmer than average in the South Pacific, south of 20° S.
Product code: IDCKSPTCSO
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