The Department of Environment and Science (DES) monitors sea-surface temperature (SST) anomalies in key regions of the Pacific Ocean over autumn, winter and spring, and provides objective outlooks for summer (November to March) rainfall on this basis. The Science and Technology Division of DES considers that the probability of exceeding median summer (November to March) rainfall is currently higher than normal for much of Queensland.
The most closely monitored driver of Queensland rainfall is the El Niño-Southern Oscillation (ENSO) phenomenon. Climate scientists monitor several ENSO indices, including the atmospheric Southern Oscillation Index (SOI) and SST anomalies in the central equatorial Pacific Ocean. Sea-surface temperatures in the central equatorial Pacific have cooled quite rapidly over the last three months, from near El Niño thresholds in March (+0.6°C) to a slightly negative value (-0.2°C) in May. The average SOI value over the last three months (March to May) was slightly negative (-1.4). The Bureau of Meteorology currently classify conditions as being ‘ENSO-neutral’.
At this time of year, the SST anomaly in the central equatorial Pacific does not provide a useful guide to rainfall probabilities over the coming summer. However, SST anomalies in the extra-tropical Pacific are more persistent and can provide a useful long-lead guide to summer rainfall probabilities. The current DES outlook for summer rainfall in Queensland (below) is based on an objective analysis of SST gradients in key regions of the Pacific Ocean. On this basis, the Science and Technology Division of DES considers that the probability of exceeding median summer (November to March) rainfall is currently higher than normal for much of Queensland (see map in PDF).
Sea-surface temperature anomalies in the central equatorial Pacific tend to ‘lock in’ over the winter, spring and summer seasons. This persistence provides a basis for seasonal forecasting. DES will provide updates of the outlook for summer rainfall from July to November, factoring in any change to the ENSO-related SST pattern during this period.
Readers should note that seasonal outlooks are expressed in terms of probabilities. For example, an outlook may be stated as ‘a 60 to 70 per cent probability of above-median rainfall’. Such a statement should be interpreted as also meaning a 30 to 40 per cent probability of below-median rainfall. In cases where outcomes with a high probability may be more likely, this does not mean that less probable events will not occur in any given year.
For further information, please contact Ken Day: at email@example.com