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.
Near average number of tropical cyclones likely in the western South Pacific in 2021–22
- The increased likelihood of La Niña in the tropical Pacific Ocean has influenced this year’s tropical cyclone outlook.
- Even if La Niña doesn't develop, some La Niña-like effects can still occur as tropical Pacific climate indicators approach La Niña thresholds.
- Above-average number of tropical cyclones are expected in the western South Pacific region this season (based on 59% probability), with a high level of accuracy.
- Near-average tropical cyclone numbers are also likely for the eastern South Pacific but model accuracy is very low.
The South Pacific tropical cyclone season is typically from 1 November to 30 April. The average numbers of tropical cyclones during the season in the western and eastern regions are four and six, respectively. Tropical cyclones affect Pacific island countries in most years and can impact coastal regions even when they remain well offshore.
This outlook is based upon the status of the El Niño–Southern Oscillation (ENSO) during July to September 2021. ENSO has been in a neutral state since March 2021, with sea surface temperatures cooling over the past two to three months. Climate models continue this cooling trend over the coming months, with three of seven models surveyed by the Bureau meeting La Niña criteria, while another two models briefly touch La Niña thresholds. The recent cooling combined with model outlooks mean a La Niña WATCH is currently in place. In the past when La Niña WATCH has been reached, a La Niña event has subsequently developed around 50% of the time.
Ocean temperatures are currently near to above average across the southwestern Pacific Ocean. Climate models predict waters across this region will remain warmer than average in the coming three months, marginally increasing the likelihood of tropical cyclones developing.
Product code: IDCKSPTCSO
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