Monthly Climate Statement for April 2020
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. Over the last three-month period (January to March), SSTs in the central equatorial Pacific Ocean have been warmer than average (+0.5°C) and the average value of the SOI has been slightly negative (-2.7). Whilst the SST anomaly in the Niño 3.4 region is close to El Niño thresholds, the Bureau of Meteorology currently classify conditions as being ‘ENSO-neutral’.
At this time of year, the ENSO phenomenon tends to be in a state of transition. As such, the relationship between ENSO indices and subsequent winter, spring and summer rainfall is very weak. However, SST anomalies in the extra-tropical Pacific tend to be more persistent and are strongly related to rainfall in Queensland over the following summer. The current DES outlook for summer rainfall in Queensland is based on an objective analysis of this extra-tropical SST pattern. 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).
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. 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 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 ken.a.day@des.qld.gov.au
