Summer set to close on a rainy note for much of NZ

New Zealand is heading into a warm, dry summer, with much of the country likely to face significant dryness, except the northern North Island, which is expected to see a rainy end to the season.

Earth Sciences New Zealand’s summer outlook, presented by principal scientist Chris Brandolino, forecasts above-average temperatures for the western and upper North Island and the upper South Island. Brandolino said dryness across the country was a growing concern.

Despite the overall hot, dry pattern, the upper North Island is expected to buck the trend, with increased rainfall forecast for late summer. Brandolino described the coming months as a “summer of two personalities,” Stuff has reported.

According to a report by Stuff, he said there was a 65% chance of above-average temperatures for the top of the country, Waikato, Bay of Plenty, Auckland, Northland and Coromandel. The western and upper North Island, and the upper South Island, also had elevated chances of warmer weather, though slightly lower at 55%.

Brandolino highlighted that New Zealand was experiencing “significant to severe marine heatwave conditions,” contributing to warmer air temperatures and increased humidity, as reported by Stuff.

“If our ocean temperatures are running warmer than average, then our air temperatures are very likely going to be warmer than average,” he said, Stuff reported.

“It will have an upward influence on temperatures, especially at night, which will increase the humidity, make it feel more uncomfortable,” Stuff has quoted.

This effect would be most noticeable in the North Island. Brandolino noted that coastal waters in the northwest of the upper North Island were unusually warm, three to four degrees above normal, sitting at roughly 20°C.

“You don’t see temperatures this warm typically in late November, early December,” he said. “Highly unusual,” Stuff has quoted.

Warmer oceans also fuel higher humidity and water vapour, increasing the potential for heavy rainfall.

“That does load the dice for big rain events. Something like this is more likely to occur in the second half of summer,” Stuff has quoted.

As a result, the upper North Island was likely to see normal or above-normal rainfall, particularly later in the season.

For the rest of the country, temperatures were expected to be average or above average. The South Island could expect some cooler snaps in December, preventing the season from being classified as entirely above average, despite several days already reaching or exceeding 30°C.

Earth Sciences New Zealand also warned of extended dry spells.

Brandolino said last summer’s dryness in the western and lower North Island remained an area of concern, with the South Island also at risk.

“What there is is a pretty overwhelming theme for much of the country for dryness,” as quoted by Stuff.

Although some rain is expected in the short term, Brandolino said it was not likely to set the tone for the season.