Monthly Climate Statement for October 2024
The Department of Environment, Science and Innovation (DESI) 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 since March this year, the Science Division of DESI 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.
The most recent three-month average value of the SOI* is near-average (+0.1 for July to September) and the corresponding SST** anomaly in the Niño 3.4 region of the central equatorial Pacific is average (+0.0°C). On this basis, the Bureau of Meteorology (BoM) currently classifies the state of the ocean and atmosphere as ENSO-neutral.
Most international climate models are projecting below-average SSTs in the central equatorial Pacific during the lead-up to summer. The BoM ENSO Outlook currently (as at 21 October) remains at ‘La Niña Watch’, but with a slightly reduced chance of La Niña developing compared to previous outlooks.
The current DESI outlook for summer rainfall in Queensland is an objective analysis of historical conditions using indices based on SST anomalies measured in key regions of the tropical and extra-tropical Pacific Ocean, which have been related to rainfall over much of Queensland in the following summer. On this basis, the Science Division of DESI considers that the probability of exceeding median summer (November to March) rainfall is currently greater than 70 per cent for much of Queensland, which is higher than the normal probability of 50 per cent (see map in PDF).
ENSO-related SST anomalies, whether cool or warm, tend to build in the central Pacific over winter and spring and then persist over summer, providing a basis for seasonal forecasting. The current outlook for summer factors in the evolving ENSO-related SST pattern and further updates will follow each month from October to November.
Readers are reminded that seasonal outlooks are expressed in terms of probabilities. The probabilities shown on the rainfall outlook 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. An analysis may, for example, indicate that below-median summer rainfall occurred in most of those years. However, this also means that summer rainfall was at, or above, the long-term median in some of those years. Therefore, an outlook which states that there is ‘an 80 per cent probability of below-median rainfall’ should also be interpreted as there being ‘a 20 per cent probability of median or above-median rainfall’.
For more information, please contact Stuart Burgess at: stuart.burgess@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 NINO3.4 1991-2020 base period)
