2023 so far: NZ's record-breaking weather

It was the wettest first half of the year on record for several areas in the northern and eastern North Island.

NIWA meteorologist Ben Noll says that to many, the results probably won't be a surprise.

"Those living in Northland, Auckland, the Coromandel Peninsula, Gisborne, and Hawke's Bay have dealt with a constant barrage of sub-tropical lows, atmospheric rivers, and ex-tropical cyclones, which caused copious amounts of rainfall. It has been quite relentless," said Noll.

In terms of temperature, January-June 2023 was 1.1˚C above average, according to NIWA's seven station temperature series which began in 1909. This is the second warmest such period on record. Only 2016 had a warmer January-June.

La Niña: even though it officially ended earlier in the year, the lingering influence of La Niña contributed to an air pressure pattern that brought more sub-tropical, north-easterly winds, atmospheric rivers, and increased the risk for ex-tropical cyclones.

Southern Annular Mode: persistent "blocking" high pressure near the South Island enabled rain-bearing weather systems to linger for long periods of time, sometimes affecting the same regions day after day.

Marine heatwaves: frequent air flows from the north-east, reduced westerly winds, high pressure near the South Island, and climate change enabled this driver to bring warmer temperatures and increased moisture availability to the New Zealand region.

Climate change: the impact of climate change left a strong imprint on the record warmth and exacerbated the extreme rainfall events during the first half of the year.

El Niño is emerging in the tropical Pacific and is expected to bring notably different weather patterns to the country during the back half of the year as compared to the first half.

During late winter, spring, and summer, southwesterly-to-westerly winds will become more prominent. Historically, this has increased the chance for drier-than-normal conditions in eastern areas of the country and caused more rain in the west.

"In summary, a change in the climate driver means a change in the wind, and ultimately, a likely change in rainfall patterns. The weather is likely to be quite different to what we've been living through in recent times," said Noll.

Record rainfall in the first half of 2023

This table shows the 21 locations* across seven different regions that experienced a record wet January-June.