THE Pacific Ocean is showing signs that it could be shifting towards La Nina, a pattern of wind and ocean temperatures that typically boosts rainfall in large parts of Australia, including inland NSW.
La Nina is one of three phases of a cycle called the El Nino-Southern Oscillation (ENSO). Each phase of the ENSO cycle - La Nina, neutral and El Nino - refers to a distinct pattern of sea surface temperatures and wind across the equatorial Pacific Ocean.
All three phases of ENSO affect the world's climate and weather in different ways.
In Australia, the state of ENSO can mean the difference between a year dominated by drought or floods.
La Nina occurs when trade winds strengthen over the Pacific Ocean, causing cooler-than-average water to develop in the central and eastern tropical Pacific Oceans, while unusually warm water builds up in the western tropical Pacific.
This pattern typically enhances rainfall in large areas of eastern and northern Australia, particularly in winter and spring.
It also increases the likelihood of below-average daytime maximum temperatures over most of Australia outside the tropics, particularly during the second half of the year.
The Pacific Ocean is currently in a neutral phase.
However, there is a clear pattern of cooler-than-usual seas over the eastern half of the equatorial Pacific and warmer-than-usual seas over western tropical Pacific.
This pattern is La Nina-like.
However, it will need to persist and strengthen further over the coming months to develop into a proper La Nina event.
Some international forecast models suggest that the Pacific Ocean will continue to trend towards La Nina during the rest of Australia's winter and early spring.
In response to these signs, the Bureau of Meteorology increased its ENSO Outlook to La Nina Watch this week.
This means there is a 50 per cent chance of La Nina developing later in the year, which is roughly double the normal likelihood.
It's too early to tell whether or not we are in the early phase of the world's next La Nina episode. But with the current state of the Pacific Ocean, and clear signs some forecast models are heading further this way, the odds of La Nina developing later in 2020 are increasing.
More information will become available as the Pacific Ocean continues to evolve, hopefully giving us a better idea of what to expect later in the year.
