NZ weather: Abnormal El Niño weather likely this summer

While many parts of the country have been drenched this week, forecasters say an abnormal El Niño weather event is looking likely for New Zealand over summer.

In the latest update about the potential for an El Niño system, NIWA meteorologist Ben Noll said there was now an 80 percent chance it will happen.

"El Niño conditions have still yet to officially arrive, but the Pacific Ocean continues to make strides towards it," he said.

He said this particular El Niño is likely to start late, and is exhibiting some non-traditional characteristics in the ocean.

"The most unusually warm sea surface temperatures are in the central equatorial Pacific - typically, they are found further east, closer to South America," said Mr Noll.

This is known as a central-based El Niño, or El Niño Modoki. Modoki is a Japanese word that means "same, but different".

He said impacts from this El Niño are likely to deviate from those experienced during a conventional event.

"During summer in a typical El Niño, New Zealand has stronger and/or more frequent winds from the west, leading to an elevated risk of drier-than-normal conditions in the east of both islands and above normal rainfall in the west," he noted.

"This year and into next year, while westerly air flow patterns are favoured, the summer season may come with a bit more variability."

El Niño Modoki may be associated with periodic easterly wind flows that bring some beneficial rainfall to eastern areas.

"The next three months is equally likely to have above average or average temperatures for all regions of New Zealand, with rainfall below normal or near normal for most areas," he said.

There are several regions identified by NIWA that should be monitored closely for developing dry conditions this summer season, including lower/western South Island, Gisborne/East Cape, Bay of Plenty, Coromandel/Waikato, Auckland, and Northland.

While El Niño can be confined to summer, NIWA forecasters say the chance for this to carry on into autumn is elevated and stands at 55 to 60 percent.