Monthly Climate Statement for October 2015
The Science Division of the Department of Science, Information Technology and Innovation (DSITI) considers that, for most of Queensland, there is an increased probability of below median October to December rainfall, with a similar outlook for the coming summer (November to March 2015/16). Read More (PDF, 616K, last updated 12:14PM, 15 October 2015)*
DSITI’s seasonal outlooks for Queensland are based on the current and projected state of the El Niño–Southern Oscillation (ENSO) phenomenon and on factors which alter the impact of ENSO on Queensland rainfall (i.e. the more slowly changing extra-tropical sea surface temperature (SST) pattern in the Pacific Ocean).
At this time of year, and over the coming months, the prevailing ENSO pattern, as measured by indices such as the Southern Oscillation Index (SOI) or central equatorial Pacific Ocean SST anomalies, offers a useful basis for providing seasonal outlooks for spring and summer.
Rainfall over the last three-month period (July to September) has been well-below average (less than the 20th percentile) across much of central and south-western Queensland, and close to average in many southern and southern-eastern parts of the state.
Currently:
- The monthly value of the SOI was -19.0 in August and -16.7 in September, remaining negative for the 16th consecutive month. As at 13 October, the 30-day mean SOI value was -22.1 and the 90-day mean value was -19.0.
- The monthly SST anomaly in the Niño 3.4 region of the central equatorial Pacific Ocean warmed from +2.06 ºC in August to +2.28 ºC in September. As at 10 October the weekly SST anomaly in the Niño 3.4 region was +2.4 ºC, the highest since the strong El Niño of 1997-98 (when +2.7 ºC was reached).
- Most international global climate models indicate that the current warming observed in central equatorial Pacific Ocean SSTs should peak over of summer.
What if the El Niño continues?
Currently, 80 per cent of Queensland remains drought declared under state government processes (see map, below). The high probability of the current El Niño event continuing further into spring and, with it, the threat of another dry summer for some regions, poses a risk of current drought conditions becoming more protracted. This risk should be factored into decision making and allocation of resources. In this context, DSITI’s long-lead outlook for summer rainfall (opposite page) should be taken into consideration.
Rainfall over the last three-month period (July to September) has been well-below average (less than the 20th percentile) across much of central and south-western Queensland, and close to average in many southern and southern-eastern parts of the state.
Seasonal rainfall outlook (Oct-Dec 2015)
Based on previous years when the SOI has been in a ‘Consistently Negative’ phase at the end of September, the probability of rainfall being above median for the next three-month period (October to December) is less than 40 per cent for most of Queensland (see map below). However, for southern and western parts of the state the probability of above median October to December rainfall is marginally higher (40 to 50 per cent).
Summer rainfall outlook (Nov-Mar 2015/16)
DSITI scientists have shown that extra-tropical SST anomalies, when measured in specific regions of the Pacific Ocean in March each year, provide a useful basis for long-lead forecasting of summer (November to March) rainfall in Queensland. The accuracy of this outlook increases as the evolving ENSO-related SST pattern is also taken into account from May through to October. This understanding has been incorporated in an experimental system known as SPOTA-1 (Seasonal Pacific Ocean Temperature Analysis version 1), which has been operationally evaluated by DSITI scientists for over a decade.
As at 1 October 2015, DSITI’s updated long-lead outlook for the coming summer (November to March 2015/16) continues to indicate a lower than normal probability of exceeding median rainfall for most of Queensland, based on the evolving sea surface temperature pattern across the Pacific. A final assessment of rainfall probabilities for summer will be made in November.
It should be noted that:
- The current long-lead outlook is based on extra-tropical and central equatorial Pacific Ocean SST anomalies, and factors in the most recent ENSO developments.
- The current El Niño pattern is likely to persist over summer (November to March).
- An increased risk of below-median rainfall for Queensland means that there is also a low probability of widespread drought-breaking rainfall. However, this does not rule out the possibility of localised high rainfall events or mean that below-median rainfall will occur throughout all of the state.
The Bureau of Meteorology provides advice on the tropical cyclone season (November to April). As at 12 October, the Bureau advises that, “While El Niño is typically associated with fewer cyclones and a later start to the season, there has never been a cyclone season without at least one tropical cyclone crossing the Australia coast” (see 12 October 2015-16 Newsroom release).
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