Monthly Climate Statement for April 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 March SST pattern in the Pacific Ocean, the Science Division of DES considers that the probability of exceeding median summer (November to March) rainfall is currently near-normal for most 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 most recent three-month average value of the SOI* was quite positive (+6.7 for January to March), reflecting the La Niña conditions that prevailed over summer. The corresponding average value of the SST anomaly in the Niño 3.4 region** was -0.4°C for January to March. Autumn is known as a period when El Niño and La Niña events tend to break down, and March has seen a moderating of both the SOI and Niño 3.4 region SST anomalies.
The current DES outlook for summer rainfall in Queensland is based on an objective analysis of SST anomalies measured in March, in key regions of the extra-tropical Pacific Ocean. On this basis, the Science Division of DES considers that the probability of exceeding median summer (November to March) rainfall is currently near-normal (between 30 and 70 percent) for much of Queensland (see map in PDF).
SST 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. Many international climate models currently project warming of SSTs in the Niño 3.4 region over winter and spring, and the Bureau of Meteorology ENSO Outlook is currently set at ‘El Niño Watch’. DES will provide an updated outlook for summer rainfall in June, at which time this outlook will begin to factor in the evolving ENSO-related SST pattern.
Readers are reminded that seasonal outlooks are expressed in terms of probabilities. The probabilities shown in the 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 Ken Day at: ken.a.day@des.qld.gov.au
* www.longpaddock.qld.gov.au/soi/soi-data-files (monthly SOI 1887-1989 base period)
** www.cpc.ncep.noaa.gov/data/indices (monthly OISST.v2.1 1991-2020 base period)
