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What a late El Nino may bring

Ben Domensino, Friday September 14, 2018 - 12:17 EST

An El Nino event could be on the cards before the end of 2018, although it might not have the effect on rainfall that many Australians expect.

Australia and other international forecasting organisations predict that there's about a 50-65 per cent chance of El Nino developing later this year.

El Nino occurs when there's a change in the typical pattern of sea surface temperatures across the equatorial Pacific Ocean.

During El Nino, we usually see warmer than usual water sitting off the west coast of South America and cooler water in the western Pacific, near northern Australia. This pattern alters the atmospheric circulation across the region, which usually causes below average rainfall in much of northern and eastern Australia during winter and spring.

However, El Nino's influence on rainfall in eastern Australia tends to diminish from about November onwards. During summer, El Nino's are just as likely to cause more rain than less rain in many parts of the country. One exception to this is the nation's eastern tropics, where dry conditions are still favoured during and El Nino summer.

So what does this mean for the months ahead here in Australia?

El Nino events usually start and end during autumn. If an event does begin this year, it will be kicking off later than usual and this may affect its influence.

A late forming weak El Nino could have little effect on rainfall in eastern Australia, particularly during the summer months. Further north, the nation's tropics may see a reduction in early-season rainfall if El Nino does develop. This has been reflected in the forecast of a late Northern Rainfall Onset for most of northern Australia this season.

A number of climate models also suggest that an El Nino may be weak if it develops. However, this does not necessarily mean that its impacts will be lessened. Some weak El Nino events in the past have had a strong effect on Australian rainfall, for example in 2006/07 and 2002/03.

Nothing is guaranteed during an El Nino, although they don't always mean dry weather in Australia. Check the latest seasonal outlooks from the Bureau of Meteorology to see what's expected to occur around the country in the months ahead.

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