Hot and humid July is one for the record books

Aotearoa, New Zealand, just endured its wettest July yet, and fourth warmest, according to NIWA.

Flooding at the intersection of Bellbrook Crescent and Emmett Street in Shirley, Christchurch.

A street flooded in the Christchurch suburb of Shirley last month.
Photo: RNZ/Niva Chittock

In its monthly summary, the National Institute for Water and Atmospheric Research (NIWA) said that from July 11 to July 31, five separate weather events generated enough rain to cause flooding around the motu.

The culmination of these frequent rain events led to 20 centers experiencing their wettest July on record and near-record wet months in 25 other locations.

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

A slip on Volga Street in the Wellington suburb of Island Bay.

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

The exceptions were the coastal parts of Gisborne, Hawke’s Bay, and the northern Wairarapa, which experienced below-normal rainfall.

in Christchurch, it was the wettest month (of any month) on file. The 310mm of rain recorded there was the first time more than 300mm of rain had fallen in a month since records began in 1863. It represented about half of the rainfall the city typically received over the course of a year.

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

Frequent wet weather meant it was also an overcast month and this was reflected in warmer than usual overnight temperatures, with both the North and South Islands experiencing record or near-record mean (overnight) minimum temperatures.

Overall, it was New Zealand’s fourth warmest July on record, with the national 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 the NIWA Snow and Ice Network, reported snow depths during July that were the deepest for the time of year since the start of the storm. registration in 2010.

NIWA said the hot, humid weather was the result of a general air pressure pattern that saw higher-than-usual pressures in the northeast and southwest of the country and was associated with airflows further north (air mass origin Warm and wet).

Council contractors cleaning stormwater drains in Edgeware, Christchurch, July 26, 2022.

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

The prevailing pressure configuration allowed consecutive low pressure systems to approach from the northwest, which were supplied by tropical moisture flows from the Coral Sea.

High pressure to the north-east of the country prevented low temperatures from rapidly receding and resulted in prolonged rains, in contrast to systems in the south and south-west, which are more characteristic of New Zealand winters.

La Niña also influenced the weather system, bringing more northerly airflows and contributing to warm sea surface temperatures that can help trigger approaching storms.

Other highlights:

  • The highest temperature was 22.6°C, observed at Bromley on July 14.
  • The lowest temperature was -11.6°C, observed at Aoraki/Mt Cook Airport on July 17.
  • The highest rainfall in 1 day was 371 mm, recorded in the town of Aoraki/Mt Cook on July 18.
  • The highest wind gust was 198 km/h, observed in Waipara West on July 9.
  • Of the top six centers, Auckland was the warmest, Christchurch the wettest, Hamilton the driest, Tauranga the sunniest and Dunedin the coldest and least sunny.
  • Of the available sunlight observing sites that report regularly, the four sunniest regions so far are Taranaki (1539 hours), Bay of Plenty (1478 hours), Greater Nelson (1462 hours) and Kāpiti Coast (1409 hours)
Niwa July 2022 weather information

Photo: Supplied / Niwa

Niwa July 2022 weather information

Photo: Supplied / Niwa

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