The likelihood of an El Nino forming during the coming months has increased this week, according to the latest outlook issued Bureau of Meteorology.

On Tuesday, the Bureau issued an El Nino Alert, meaning there is a 70 per cent chance of an El Nino event occurring during the coming months. This likelihood is up from a 50 per cent chance at the beginning of March.

Sea surface temperatures in the equatorial Pacific Ocean have been in an El Nino-like pattern for the last few weeks. If this pattern is sustained during the coming months, it will increase the likelihood of the atmosphere becoming coupled with the ocean, which is necessary for an El Nino event to be declared.

Most international computer models indicate that warming in the equatorial Pacific Ocean will continue until at least winter, suggesting that an El Nino event could be getting underway. However, it's worth noting that computer models have less accuracy predicting El Nino at this time of year, so there's a fair degree of uncertainty in this outlook.

El Nino events often cause below average rainfall in eastern Australia during winter and spring and above average maximum temperatures in southern Australia.

The potential for El Nino during the middle of this year increases the likelihood of below average winter-spring rainfall over inland areas of NSW. However, it's certainly not guaranteed at this point. More accurate outlooks will become available closer to winter.