The first half of the year has been among the hottest on the books, and temperatures on the warmer side of average are forecast to roll on through to early spring.
Meteorologists crunching data on the first six months of 2019 expect it will place within the top 10 warmest – and would have been in the top five if not for a series of chilly mornings last week.
Niwa's climate outlook for July to September, released today, has picked average to above-average temperatures, thanks to the same background drivers that have been influencing weather conditions for two years.
Those included an unusual but weak El Nino climate system and a Southern Annular Mode (SAM) in a positive phase, which brought fewer cold fronts.
Both had contributed to warmer sea surface temperatures surrounding New Zealand, which in turn delivered higher temperatures to the mainland.
Over the past month, seas were more than 0.7 above average, for the fourth consecutive month.
"As long as those sea surface temperatures remain above average around the country, we are going to be hard pressed to get a month that is below average," Niwa meteorologist Ben Noll said.
"The SAM has been very positive for the better part of the last two years, and we've also been seeing this atypical El Nino event that's been located in the Central Pacific – if we had a more typical one, we would be more exposed to some cooler sea surface temperatures.
"And of course, what's underneath it all and driving that long-term average up is global warming.
"A lot of that warming has been absorbed in the ocean, and we're now just less likely to see those cooler seas as often as we did even a decade or two ago."
The outlook predicted the El Nino would stay in place over the next three months, but might gradually weaken and become less influential.
Over the same time, air pressure was expected to be higher than normal to the northwest of New Zealand and lower than normal to the south, with more westerly winds first but then mixed flow patterns later.
Source / NIWA
Warm spells were possible on occasions during this month, and particularly next month, when air flows reached out from Australia from time to time.
Niwa expected rainfall levels would be either near or below normal in the north of the North Island and north and east of the South Island, but near normal elsewhere.
Noll said there might be a trend toward more unsettled weather at the back-end of the period, particularly in September.
"As we go later into the season, there is an indication that the weather will progressively and generally become more active, with September a possible stand-out."
Despite a low chance for below-average seasonal temperatures, cold snaps and frosts still remained likely over coming months.
But the overall picture wasn't one that skifield operators would be happy with.
"They're certainly not going to like what's coming this week – that's a northerly flow – so anything that's on the slopes is probably going to melt away as we go into the weekend," Noll said.
"Later on in the season, there will be some moisture at those higher elevations – but what we really need is one of those big southerlies, and that just doesn't look to be on the cards for the next little while."
Source / NIWA
Noll said Niwa expected to release data for the first half of the year – which had already included the fourth warmest autumn and third warmest summer on record – tomorrow.
"June was running at above average for the first three weeks, but then last week we had some chilly mornings last week, which has driven down the anomaly a bit," he said.
"So I'd say we'd be looking somewhere between the fifth and seventh warmest [first six months]."
AT A GLANCE: JULY TO SEPTEMBER
• Temperatures are forecast to be near average or above average everywhere, owing to warmer-than-average coastal and regional sea surface temperatures. • Warm spells are possible on occasions during July and particularly August when air flows extend from Australia from time to time. • Rainfall is forecast to be near normal or below normal in the north of the North Island and north and east of the South Island. Near normal rainfall is forecast in all other regions.
