In comparison, Waimate in South Canterbury received just 30 per cent of its normal annual rainfall in the same period.
Temperatures over that same period were 1.1C 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.
The 11 locations that recorded over a year’s worth of rain in the first six months of 2023:
- Kaikohe (2140mm)
- Whangārei (1526mm)
- Warkworth (1525mm)
- Leigh (1234mm)
- Whangaparāoa (1114mm)
- Albany/North Shore (1319mm)
- Māngere (1152mm)
- Tauranga (1335mm)
- Gisborne (1230mm)
- Tūtira (1359mm)
- Napier (984mm)
What’s behind the rainfall?
MetService forecaster Lisa Murray said climate change, a marine heatwave and La Nina were all partly to blame.
Although La Nina officially ended earlier in the year, the lingering influence contributed to an air pressure pattern that brought more sub-tropical, northeasterly winds, atmospheric rivers and increased the risk for ex-tropical cyclones.
Persistent “blocking” high pressure near the South Island enabled rain-bearing weather systems to linger for long periods, sometimes affecting the same regions day after day.
Frequent airflows from the northeast, reduced westerly winds, high pressure near the South Island and climate change enabled this situation to bring warmer temperatures and increased moisture availability to New Zealand.
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, Niwa said.
“All these things have combined along with a bit of being unlucky as well, because they could have gone a little way east, they could have gone westwards, but actually they came down over New Zealand,” Murray said.
“So we have the situation where we’ve had event after event after event. Some of those regions are very saturated even still.”
What’s to come?
MetService has forecast more rain for the east from Sunday.
El Nino is emerging in the tropical Pacific and is expected to bring different weather patterns during the next six months.
“The systems we have coming through at the moment, and continuing really for much of July, are very fast-moving systems. So although they will come in and bring some heavy rain, they will move through quickly,” Murray said.
During late winter, spring and summer, southwesterly to westerly winds will become more prominent.
Historically, this had increased the chance for drier-than-normal conditions in eastern areas of the country and caused more rain in the west, Niwa said.
“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,” Niwa meteorologist Ben Noll said.
