El Nino does not always mean dry weather
El Nino is synonymous with drought in Australia. The Pacific Ocean climate driver typically contributes below average rainfall across most of eastern Australia during the middle of the year and has underscored some of our nation's worst dry periods in history.
In its latest El Nino Southern Oscillation (ENSO) outlook issued at the end of July, the Bureau of Meteorology estimated that there is a 50 per cent chance of El Nino developing during the second half of 2018. Some international organisations, such as America's Climate Prediction Centre, put the odds of El Nino even higher, reaching up to 70 per cent during Australia's summer.
Based on an analysis of 12 typical El Nino events between 1905 and 1998, rainfall across most of eastern Australia - including all of NSW west of the divide - is usually in the bottom 20-30 per cent of historical records between June and November, when El Nino is in play.
However, every El Nino is different and their effects on rainfall can be difficult to predict.
El Nino events typically start and end during Autumn and have their greatest correlation with Australian rainfall during winter and spring. However, the influence of typical El Ninos on rainfall in Australia diminishes from November onwards.
In fact, above average rainfall has been know to fall across eastern Australia during summer and autumn in some late-starting El Ninos. This was the case as recently as 2009/10.
While it's not a time to be overly optimistic about rainfall in the months ahead, it's worth pointing out that the potential for El Nino during the second half of 2018 does not necessarily mean that the dry weather currently gripping NSW is destined to continue.