SunLive – Record heat so far this winter
New Zealand has just had its warmest June and July since record breaking began in 1909 and – one month to go – is on track for its second consecutive warmest winter on record.
Data from the temperature series from NIWA’s seven stations show that the temperature for the past two months was extremely high, 1.53 ° C above the long-term average.
NIWA meteorologist Ben Noll said the previous record was 1.15 ° C above average for the months of June and July 2016.
“There have been a number of factors that have contributed to the warmer temperatures. Air pressure has been higher than normal in the east so far this winter, which has brought more northeast winds. in New Zealand, bringing warmer air from the subtropics. “
Sea temperatures around the coast have also been warmer than average, altering cooler air masses moving towards New Zealand.
Ben says the southern hemisphere polar vortex over Antarctica has been stronger than normal.
“It helps keep the strands of freezing air at the bottom of the Southern Ocean.”
Atmospheric models have also leaned in a direction similar to that of La Niña, which tends to produce warmer conditions in the Southwest Pacific.
Another climatic factor in the Indian Ocean, called the Indian Ocean Dipole, developed in July and played a role in the atmospheric river which caused flooding in the Buller district as well as heat and additional moisture.
Meanwhile, warmer temperatures have resulted in more rain and less snow at lower elevations where rain has taken its toll in some ski areas.
Hydrological forecaster Dr Jono Conway said most NIWA snow monitoring stations between 1,800 and 2,000 m elevation experienced average or above average snow levels for the time of year, but lower elevation sites had little or no snow.
Aside from the Canterbury sites which received a heavy snow dump at the end of the May flood, most of the snow comes from a few large events in early to mid-July.
“The warm temperatures caused the precipitation to fall in the form of rain at lower elevations, making it very difficult for ski areas with bases at lower elevations, especially club grounds without snow.”
July in particular had above or much above normal precipitation in the interior and west of the South Island, with Mount Cook recording 146% of its normal monthly precipitation and Arthur’s Pass 181%.
Monthly temperatures were 1.7 ° C and 1.9 ° C above average respectively, illustrating that the rain / snow zone was at a higher than normal elevation.
Ben says that with temperatures well above average in June and July, this winter was way ahead of last year’s numbers.
“This is in line with our expectations. Against the backdrop, the long-term tailwind of climate change continues to turn. Of the seven hottest months of June and July, six have occurred since 2000,” Noll said. .
For the year until the end of July 2021, it ranks sixth hottest on record.