Wet, warm July proves one for record books

Aotearoa New Zealand just experienced its wettest — and fourth warmest — July on record, NIWA says.

In its July 11-31 monthly summary, the National Institute of Water and Atmospheric Research (NIWA) said five separate weather events have generated enough rain to trigger flooding around the motu.

The culmination of these frequent downpours led 20 centers to experience their wettest July on record and near-record wet months for another 25 sites.

The vast majority of the country had well above normal rainfall, with Wellington and Dunedin experiencing their wettest July on record, while Auckland and Hamilton saw their second and third wettest respectively.

A slip in Island Bay after heavy rain in Wellington last month.
Photo: RNZ / Craig Stephen

The exceptions were coastal areas of Gisborne, Hawke’s Bay and northern Wairarapa, which saw less than usual rainfall.

In Christchurch it was the wettest month (of any month) on record. The 310mm of rain recorded there marked the first time more than 300mm of rain fell in a month since the measurements began in 1863. It represented about half of the rain the city normally receives over the course of a decade. received a year.

It’s official: July 2022 is Christchurch’s wettest month on record with 266mm of rain

Since registration began in 1864, more than 200mm of rain fell in just 15 months of a total of 1,739.

Christchurch has had about 43% of the annual normal rainfall in July! pic.twitter.com/FA3A1usRjc

— NIWA Weather (@NiwaWeather) July 28, 2022

However, it was also warm, especially in the North Island, where temperatures were well above average and many centers are experiencing record or near-record heat.

Frequent wet weather meant it was also a cloudy month and this was reflected in warmer than usual nights with both the North and South Islands experiencing record or near record high mean minimum temperatures (at night).

Overall, it was New Zealand’s fourth-warmest July on record, with a nationwide average temperature (9.9 degrees Celsius) 1.3 degrees Celsius above average, NIWA said.

Some high-altitude weather stations, such as Mueller Hut (in Aoraki/Mt Cook National Park) in NIWA’s snow and ice network, recorded snow depths in July that were the largest for the time of year since recording began in 2010.

NIWA said the wet, warm weather resulted from an overall higher-than-usual barometric pressure pattern in the northeast and southwest of the country and was associated with more northerly air currents (warm and wet air mass origins).

Workers attempt to clear gutters at Edgeware in Christchurch during heavy rain last month.
Photo: RNZ / Niva Chittock

The dominant pressure arrangement allowed successive low-pressure systems to approach from the northwest that were fed by streams of tropical moisture from the Coral Sea.

High pressure in the northeast of the country prevented the lows from quickly dissipating and resulted in prolonged rainfall – a contrast to the southern and southwestern systems more characteristic of New Zealand winters.

La Niña also impacted the climate system, pushing more air currents to the north and contributing to warm seawater surface temperatures, which may help stimulate incoming storms.

Further highlights:

• The highest temperature was 22.6degC, observed in Bromley on July 14
• The lowest temperature was -11.6°C, observed at Aoraki/Mt Cook Airport on July 17
• The highest one-day rainfall was 371mm, recorded in the village of Aoraki/Mt Cook on July 18
• The highest wind gust was 198 km/h, observed at Waipara West on July 9
• Of the six main centres, Auckland was the warmest, Christchurch the wettest, Hamilton the driest, Tauranga the sunniest and Dunedin the coldest and the least sunny
• Of the available, regularly reporting solar observing sites, the sunniest four regions to date are Taranaki (1539 hours), Bay of Plenty (1478 hours), Greater Nelson (1462 hours) and Kāpiti Coast (1409 hours).

Photo: Delivered / Niwa

Photo: Delivered / Niwa