After months of anticipation, the Bureau of Meteorology officially declared an El Niño on June 16.

El Niño is a naturally occurring variation in temperature and winds across the Pacific Ocean that can influence weather around the globe.

During El Niño, sea surface temperatures in the central and eastern Pacific warm up and trade winds – which typically blow from east to west along the equator – weaken. As a result, a region of strong storm activity known as the Walker Circulation shifts east over the Pacific Ocean, drawing moisture and clouds away from Australia.

Past El Niño events have coincided with some of the driest and hottest weather in Australian history.

Making El Niño official

El Niño events occur about every three to seven years, and can last anywhere from six months to two years. They typically ramp up in winter and spring, before easing in autumn.

The likelihood of El Niño has been in the news for months, but the Bureau of Meteorology only just officially declared it active. That’s because there is a specific set of criteria that must be met.

Scientists must observe at least three of the following:

Sea surface temperatures in the central Pacific Ocean must be greater than 0.8°C above average

Sea surface temperatures in the central Pacific Ocean must be greater than 0.8°C above average

The trade winds that blow east to west across the Pacific have to be weaker than average for the........

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