Monthly climate statement for May 2018
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 Division of DES considers that the probability of exceeding median summer (November to March) rainfall is currently slightly higher than normal for much of Queensland. Read more (PDF)
DES provides seasonal outlooks for summer rainfall in Queensland based on SST anomalies in key regions of the Pacific Ocean. The current outlook is based on SST anomalies in the extra-tropical Pacific Ocean. Unlike SST anomalies in the equatorial Pacific, which are strongly related to the El Niño-Southern Oscillation (ENSO) phenomenon, early-autumn (i.e. March) SST anomalies in the extra-tropical Pacific tend to persist through to summer and provide a useful basis for providing an initial long-lead outlook of summer rainfall in Queensland.
At this time of year the ENSO phenomenon tends to be in a state of transition. For this reason, ENSO indices such as the Southern Oscillation Index (SOI) and SST anomalies in the equatorial Pacific, do not provide a useful indicator of summer rainfall. The Bureau of Meteorology consider that the La Niña pattern which persisted over spring and summer has now returned to a neutral state. Although SSTs in the equatorial Pacific remain cooler than normal (-0.4°C in April and -0.7°C from February to April), the atmospheric SOI has been in the neutral range over the last three months, averaging +1.6 for February to April.
It should be noted that seasonal outlooks are probabilistic, rather than deterministic, in nature. For example, if an outlook is described as having a 60 per cent probability of above median rainfall, there is also a 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.
As noted, DES will provide an updated outlook for summer rainfall in June. This outlook will begin to factor in the developing ENSO-related SST pattern at that time.
