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 cyclones likely in the western Pacific Ocean
- Near average number of tropical cyclones are expected in the western South Pacific region this season.
- ENSO-neutral conditions in the tropical Pacific Ocean have influenced this year's tropical cyclone outlook.
- Most climate models indicate that neutral conditions are likely to persist into 2020.
- Near-average cyclone numbers are also likely for the eastern South Pacific but model accuracy is very low.
The South Pacific tropical cyclone season typically extends between 1 November and 30 April. The average numbers of tropical cyclones during the season in the western and eastern regions are four and seven respectively. Tropical cyclones affect Pacific island countries in most years and can impact coastal regions even when they remain well offshore.
* Long-term average number of tropical cyclones, calculated using data from 1969–2018, may change slightly from one year to the next as a new season of data is added to the calculation.
This outlook is based upon the status of the El Niño–Southern Oscillation (ENSO) during the preceding July to September. Eastern tropical Pacific Ocean sea surface temperatures have cooled significantly since July and are currently close to average. The Southern Oscillation Index (SOI) was neutral through July and August and exceeded El Niño thresholds in September. However, this was primarily due to well above-average atmospheric pressure at Darwin. The corresponding pressure in Tahiti was within normal bounds, suggesting the September SOI value was not related to a developing El Niño. Other atmospheric indicators of ENSO (trade winds and cloudiness in the central Pacific) remain at normal levels. All international climate models expect Eastern Pacific Ocean temperatures to remain within neutral levels until February 2020.
The statistical model used for this outlook has a high level of accuracy predicting cyclone numbers in the western region, but a very low level of accuracy for the eastern region. This outlook is for the southern hemisphere tropical cyclone season which runs between 1 November and 30 April.
Product code: IDCKSPTCSO
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