Monthly Climate Statement for November 2023
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. Based on the evolving SST pattern in the Pacific Ocean, the Science Division of DES considers that the probability of below-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.
The average SST* anomaly in the central equatorial Pacific over the last three-month period (August to October) is +1.5°C, which falls well within the ‘El Niño’ range (>+0.5°C as recognised by DES). The average value of the SOI** over the last three-month period is -10.5, which also falls well within the ‘El Niño’ range (<-5.0 as recognised by DES).
On 19 September, the Australian Bureau of Meteorology officially declared that an ‘El Niño’ is underway in the tropical Pacific. This announcement followed earlier ‘El Niño’ declarations from both the World Meteorological Organization and the USA National Oceanic and Atmospheric Administration. Most international climate models indicate that the current El Niño pattern is likely to persist through summer.
Sea-surface temperature anomalies in the central equatorial Pacific tend to ‘lock in’ over the winter, spring and summer seasons, and this persistence provides a basis for seasonal forecasting. The current DES outlook for summer rainfall in Queensland is based on an objective analysis of SST anomalies measured in key regions of the Pacific Ocean, including those regions related to ENSO. On this basis, the Science Division of DES considers that the probability of exceeding median summer (November to March) rainfall is currently less than 30 per cent for much of Queensland (see map in PDF). This analysis also indicates a low (4 per cent) probability of wet conditions (>decile 7 rainfall) across Queensland’s main grazing district over the coming summer (November to March).
Readers are reminded that seasonal outlooks are expressed in terms of probabilities. The probabilities shown in the above map are based on an objective analysis of historical data and show the summer rainfall outcome in years when SST conditions were closest to the current year. This analysis may, for example, show that above-median summer rainfall occurred in 60 per cent of those years. However, this also means that summer rainfall was at, or below, the long-term median in 40 per cent of those years. Therefore, an outlook which states that there is ‘a 60 per cent probability of above-median rainfall’ should also be interpreted as there being ‘a 40 per cent probability of median or below-median rainfall’.
For more information, please contact Stuart Burgess at: stuart.burgess@des.qld.gov.au
* www.cpc.ncep.noaa.gov/data/indices (monthly OISST.v2.1 NINO3.4 1991-2020 base period)
** www.longpaddock.qld.gov.au/soi/soi-data-files (monthly SOI 1887-1989 base period)
