What the arrival of El Niño means for the Pacific Islands

Over the coming months, countires in the Western Pacific are likely to experience drier-than-usual conditions. Photo: Supplied/ 123rf

El Niño has been declared in the Pacific - and a forecaster says there's reason for concern.

An El Niño event occurs when the ocean becomes warmer than usual, affecting rainfall and wind patterns.

The Secretariat of the Pacific Regional Environment Programme (SPREP), which is the region's primary scientific organisation, says that sea surface temperature readings and Southern Oscillation Index values have met the thresholds for El Niño.

This means that over the coming months, countries in the Western Pacific are likely to experience drier-than-usual conditions, increasing the risk of drought.

Meanwhile, those countries in the Central and Eastern Pacific can expect above-average rainfall.

"While El Niño conditions are generally associated with drier-than-normal weather and increased drought risk in the Western Pacific, short-term heavy rainfall events can still occur within this broader pattern," SPREP said in a statement.

"Even where such events take place, monthly and seasonal rainfall totals may remain below average overall."

Earth Sciences New Zealand chief forecaster Chris Brandolino said there is reason to be concerned.

"All indications are that this will be a very strong event to perhaps something we haven't seen before, and what that means, we'll have to wait and see," he told RNZ Pacific.

"Impacts aren't always directly related to intensity, but certainly a very strong El Niño does increase the odds for higher-end impacts."

Brandolino said the expected intensity could drag on beyond the usual winter months and past September.

"It's one thing to have a dry month or two, but obviously it's a different thing to have several consecutive months of inadequate rainfall.

"Every El Niño is different ... we know the average outcome of El Niño, but no El Niño is average."

SPREP climate science director Salesa Nihmei cautioned against mistaken reporting on what an El Niño actually is.

"Past El Niño transition phases have shown that short-term weather events of this kind can create the potential for mixed messaging," he said.

"There is a risk that such events may be misinterpreted in the media, affecting how the broader El Niño outlook is understood and communicated."

The United Nations warned of a looming El Niño event at the start of the month, emerging between June and August.

The US National Weather Service in Guam has warned that the Northern Mariana Islands could see between three to five additional typh