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.
Below average number of tropical cyclones likely in the western South Pacific in 2023 to 2024
- The established El Niño in the tropical Pacific Ocean has influenced this year’s tropical cyclone season forecast.
- A below average number of tropical cyclones is likely (68% likelihood of being below average) in the western South Pacific region this season. Historical forecast accuracy for the region is low.
- A close-to-average to above-average number of tropical cyclones is expected for the eastern South Pacific (60% likelihood of being above average). Historical forecast accuracy for this region is very low.
The South Pacific tropical cyclone season typically runs from 1 November to 30 April, although tropical cyclones can, and do, form outside of those bounds. The average number of tropical cyclones during the season in the western region is 4, and in the eastern region is 6. Tropical cyclones can affect Pacific Islands and coastal regions even when they remain well offshore.
This forecast is based on the analysis of El Niño–Southern Oscillation (ENSO) oceanic and atmospheric indicators over July to September 2023. El Niño conditions were established in the tropical Pacific in September 2023. During July and August, oceanic patterns were El Niño-like but the atmospheric response to the warm sea surface temperatures in the central and eastern Pacific was weak. Climate models suggest this El Niño will persist until at least the end of February.
Ocean temperatures are currently above average across most of the Pacific Ocean, especially in the central and eastern equatorial Pacific where temperatures are at least 1.2 to 2 °C warmer than the long-term (1961–1990) average.
Product code: IDCKSPTCSO
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