July weather extremes: Floods and dry spells

Traffic backs up on State Highway 73 near Arthur's Pass during the recent flooding. Photo: NZ Herald
Traffic backs up on State Highway 73 near Arthur's Pass during the recent flooding. Photo: NZ Herald
Large areas of the country had well above normal rainfall in July, and most had above average temperatures, Niwa's climate summary reveals.

The month was the sixth-equal warmest July on record. Flood flows on the Buller River were the largest of any river in the country since 1926 after the deluge last month. The stand-out rain event between 15 July and 18 July brought over 690mm of rain to parts of the West Coast in under 72 hours.

Weather extremes in July:

  • Highest temperature: 21.0°C, observed at Whanganui on 30 July
  • Lowest temperature: -8.4°C, observed at Hanmer Forest on 4 July
  • Highest 1-day rainfall: 210 mm, recorded at Arthur's Pass on 16 July
  • Highest wind gust: 185 km/h, observed at Cape Turnagain on 18 July
  • Of the six main centres in July, Auckland was the warmest and sunniest, Wellington was the wettest, Christchurch was the driest and coolest, and Dunedin was the least sunny
  • Sunniest four locations so far in 2021 are Taranaki (1511 hours), Bay of Plenty (1481 hours), Marlborough (1477 hours), and Hawke's Bay (1446 hours) (data from available, regularly reporting sunshine observation sites).

Along with the West Coast, well above normal rainfall (more than 149 percent of normal) fell in large areas of Marlborough, Nelson, Tasman, Canterbury high country and northern Otago.

Parts of coastal northern Northland, inland Bay of Plenty and around Wellington central and the Kāpiti Coast had above normal rainfall.

In contrast the eastern North Island extending from Gisborne to the eastern Wairarapa hills, as well as coastal Canterbury from Akaroa to Kaikōura had less than half the usual rainfall.

Temperatures
The mean temperature for July 2021 was 8.9C which is 1.1C warmer than the 1981-2010 average.

Near average temperatures were observed for parts of Auckland, Bay of Plenty, parts of Waikato, inland parts of Manawatū-Whanganui, northern Hawke's Bay, Nelson, as well as patches along the eastern coastal fringe of the South Island.

Temperatures were above average or well above average for the remainder of New Zealand.

Six out of the seven warmest Julys on record have occurred since the year 2000.

Niwa meteorologist Chris Brandolino said June this year was the warmest June since records began in 1909 and the months of March to May were the 10th warmest autumn on record.

"If you put it all together, the first seven months of 2021 is the sixth warmest on record."

Climate change made extreme rain and heat events more likely, he said.

"It increases their probability of being more intense, more frequent, longer in duration."

August to October is expected to be warmer than average for all New Zealand, though there will be cold snaps.

Further ahead, forecasters are expecting a La Niña weather system to form.

 

 

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