NZ summer set to be hottest on record

Author: NZ Herald,
Publish Date: Fri, 23 Feb 2018, 11:09AM

Our scorching summer is on track to be the hottest in history.

Despite a sub-tropical storm and two ex-tropical cyclones, this summer is running at 2.3C above the 1981-2010 average.

With just five days left, unless they are unusually cold, NIWA climate scientists say this summer will surpass an 80-year-old record.

🌡️ Summer 2017-18 is expected to become New Zealand's hottest on record!

🌡️ Nationwide temperature 2.3°C above average, surpassing 1934-35.
🌡️ Driven by the #marineheatwave+#LaNiña & enhanced by #climatechange.
🌡️ 108 locations observed their hottest summer on record. pic.twitter.com/1ooVLVEmr2
— NIWA Weather (@NiwaWeather) February 22, 2018

The hottest summer recorded is 1934/35, when the temperature was 1.8C above average.

NIWA meteorologist Ben Noll says the driver has been the marine heatwave, which began at the end of November.

During different periods surface temperatures have been between 2 to 4C above average, and some areas were 6 to 7C above average.

"This represented some of the largest ocean temperature anomalies anywhere in the world over the last several months," Noll said.

A warmer-than-average Tasman Sea is a signature of La Nina, Noll said.

"It is associated with higher than normal air pressure over the region during the late-spring and early-summer.

"These conditions prevent mixing of deeper, cooler sea water to the surface.

Warm northeasterly winds also pushed warm water toward the country from the sub-tropics."

NIWA principal climate scientist Dr Brett Mullan said the 1934-35 summer showed several similarities to this summer, including widespread drought from November to mid-February.

Then New Zealand Meteorological Service director Dr Edward Kidson wrote at the time that a "feature of the pressure distribution was that the high pressure belt and tracks of moving anti-cyclones were unusually far south in the New Zealand area, generally crossing the Dominion instead of passing to the north of it."

Over land, Dr Kidson said "in none of the four months November [1934] to February [1935] did any station in New Zealand record a mean temperature which was not above normal".

Summer standouts so far

• 108 places across New Zealand recorded their hottest summer on record, 21 their 2nd hottest and eight their 3rd hottest.

• In Alexandra on January 30 the temperature reached 38.7 C. On the same day Clyde got to 37.6, Middlemarch 37.4 and Cheviot 37.3. Together these comprise the hottest temperatures of summer.

• Wellington has had 17 days above 25C this summer – the average is two.

• Auckland usually has 29 summer days above 25C, while this year there have been 47 – the highest since records began at Auckland Airport in 1966.

• Invercargill recorded three consecutive days over 30C in January. It has never done that for two days in a row, let alone three.

• Cromwell has topped 25C for 56 days – the average is 35 days.

• The dew point temperature – the meteorological measurement combining humidity and temperature – failed to drop below 19C in Auckland from February 10-15, making it a rare 115-hour period of very high humidity.

• In Wellington a dew point temperature of 22C at 6pm on February 11, the highest dew point on record for the city.

• Mahia, Appleby and Waipara West have had their wettest summers on record.

Your weekend weather

Cyclone Gita is well and truly gone and a dry, warm weekend is on the way for most providing a chance to dry out after a sodden week.

But weather analysts warn it may shortlived, as another low arrives early next week, bringing rain and gusty westerlies.

MetService meteorologist Mark Todd said Friday should be a good day in most places, with just some isolated showers, mainly in the upper North Island.

There will be a few showers also around Gisborne and Hawke's Bay, but these should clear for a good day.

Here's a look at summer pressure patterns around NZ -- watch how higher pressure in Dec gave way to a more active Tasman Sea & tropics in Jan-Feb (lower pressures), as #LaNiña + the #marineheatwave progressed. pic.twitter.com/hgJM46l5it
— NIWA Weather (@NiwaWeather) February 22, 2018

The South Island is experiencing mostly fine weather, as a southwest flow brings occasional showers to southern parts of the island.

"Everywhere else should be fine, except for a few inland showers."

Tasman, among the hardest hit districts during former Cyclone Gita's deluge on Tuesday and Wednesday, will be mostly sunny today.

For the next few days at least New Zealanders struggling with the humidity of late will be finding the cooler, drier change comforting.

"We are starting to head towards autumn. We are not quite there, but are having a taste of it after very hot summer period," said Todd.

There has even been snow down in the far south.

"Gita was a very warm, tropical system, and it met another system from the southwest, which produced snow on the Crown Range in central Otago."

Clear skies over central South Island reveals the extent of the snow about the tops of the mountains. The swirl of cloud well to the southeast of the country is what remains of Cyclone Gita. Clearing trend for the coming days, for your forecast, visit https://t.co/Yjbq0jxdqz ^HM pic.twitter.com/R2X9F8OTYp
— MetService (@MetService) February 22, 2018

Weatherwatch NZ's Philip Duncan said a new low starts to develop in the Southern Ocean from Sunday.

The low is partially fuelled by the remnants of Cyclone Kelvin, which has been crossing over Australia this week.

"This tropical rain is moving down through central Australia and will track into the Southern Ocean this weekend.

"From late Sunday and across Monday and Tuesday next week both [the North and South islands] will be affected.

"It is not a storm, but there may be some heavy rain in the west and some localised gusty winds too."