A pivot to an El Niño climate pattern should see conditions become drier in the east of New Zealand over the coming months, but the effects of the outgoing La Niña pattern may see rain linger for a few weeks yet, says NIWA meteorologist Chris Brandolino. Photo: RNZ / Rebekah Parsons-King
The shift to an El Niño climate pattern is likely to bring drier weather to eastern parts of the country over the next few months, but the threat of lingering rainfall events remains, a meteorologist says.
The National Institute of Water and Atmospheric Research (NIWA) has released its seasonal climate outlook for the next three months, indicating increased sou'westerly winds across the country and "near normal" rainfall in the east of the North Island.
"The atmosphere has a long memory" - NIWA meteorologist Chris Brandolino
An El Niño pattern - which tends to slow down, or even reverse, the trade winds that usually blow from east to west across the tropical Pacific - is taking over from the La Niña system that has driven New Zealand's weather patterns for the past three years.
NIWA meteorologist Chris Brandolino told Morning Report that would lead to more southwest winds for the country, "and with that southwest flow, areas along the west tend to be favoured for rainfall, whereas areas to the east tend to have less rain".
But that did not mean an immediate end to the types of rain events that had impacted eastern areas in recent months.
"We have this La Niña hangover," he said.
"The atmosphere has a long memory ... and the El Niño is what we call a 'coupled system', so the ocean has to be at the altar - to use a wedding analogy - and the atmosphere has to be at the altar.
"Right now, the ocean's at the altar, we're just waiting for the atmosphere to walk down the aisle and join us."
As a result, lingering rainfall events might continue to impact the eastern part of the North Island, particularly in July, he said.
But drier weather was likely on the way after that.
"Our expectation for the next three months is a good chunk of the country - two thirds of the country - may have a bit of a dry lean."
Brandolino said people should also expect more frequent southwest winds over the coming months.
"That obviously is a colder wind direction, so we'll probably find some more frequent cold snaps."
June - and indeed the past few years - had been "pretty warm", he said, so even the "near-average" temperatures NIWA was predicting for the next three months might seem cold to people.
The coming days were set to bring wind and chillier temperatures to much of the country just in time for the school holidays.
"It's just going to be a typical, quintessential windy, cold, unsettled weekend," he said.
"We'll find some heavy showers across much of the country - these waves of rain and thunderstorms; a good round of rain likely tonight for the upper North Island, so if you're travelling, keep that in mind."
However a high was forecast to move in over the country for several days from around Tuesday next week.
"That's good news because that'll settle things down," Brandolino said.
"But until then it's going to be pretty unsettled ... we'll be reminded it is winter."
NIWA's seasonal predictions for the next three months, by region
Northland, Auckland, Waikato and Bay of Plenty
- Temperatures are about equally likely to be above average (50 percent chance) or near average
- Rainfall totals are about equally likely to be below normal (45 percent chance) or near normal (40 percent
- Soil moisture levels are most likely to be near normal (40 percent chance) while river flows are
(45 percent chance).
chance). Higher than normal air pressure may build across the Tasman Sea at times, leading to spells of drier than normal weather.
about equally likely to be below normal (45 percent chance) or near normal (40 percent chance).
Central North Island, Taranaki, Whanganui, Manawatū, Wellington
- Temperatures are about equally likely to be above average (50 percent chance) or near average
- Rainfall totals are about equally likely to be below normal (40 percent chance) or near normal (35 percent chance). Higher than normal air pressure may build across the Tasman Sea, leading to spells of drier than normal weather.
- Winds may be stronger than normal, especially around the start of spring.
- Soil moisture levels are most likely to be near normal (45 percent chance) while river flows are
(45 percent chance). Marine heatwave conditions remain present in coastal waters. The warmer
than average seas may reduce the intensity of cold, southerly air masses.
about equally likely to be below normal (40 percent chance) or near normal (35 percent chance).
Gisborne, Hawke's Bay, Wairarapa
- Temperatures are about equally likely to be above average (50 percent chance) or near average
- Rainfall totals are most likely to be near normal (45 percent chance).
- The developing El Niño is expected to result in a lower likelihood of tropical moisture plumes; however, the atmosphere may still exhibit La Niña-like tendencies at times, increasing the chance for heavy rain.
- Winds may be stronger than normal, especially around the start of spring.
- Soil moisture levels and river flows are most likely to be near normal (45 percent chance).
(45 percent chance).
Tasman, Nelson, Marlborough, Buller
- Temperatures are about equally likely to be above average (50 percent chance) or near average
- Rainfall totals are about equally likely to be below normal (40 percent chance) or near normal (35 percent chance). More frequent and stronger-than-normal southwesterly quarter winds may shelter
- Soil moisture levels are most likely to be near normal (45 percent chance) while river flows are
(45 percent chance). Marine heatwave conditions remain present in coastal waters. The warmer
than average seas may reduce the intensity of cold, southerly air masses.
the region, leading to dry spells.
about equally likely to be below normal (40 percent chance) or near normal (35 percent chance).
West Coast, Southern Alps and foothills, inland Otago, Southland
- Temperatures are about equally likely to be above average (50 percent chance) or near average (45 percent chance). Marine heatwave conditions remain present in coastal waters. The warmer than
- Rainfall totals are about equally likely to be near normal (40 percent chance) or above normal (35 percent chance). Southwest quarter winds are expected to increase in frequency and strength over the
- Soil moisture levels are most likely to be near normal (45 percent chance) while river flows are about
average seas may reduce the intensity of cold, southerly air masses, especially near the coast.
period, likely bringing periods of wetter than normal conditions.
equally likely to be near normal (40 percent chance) or above normal (35 percent chance).
Coastal Canterbury and the nearby plains, east Otago
- Temperatures are about equally likely to be above average (50 percent chance) or near average
- Rainfall totals are about equally likely to be below normal (40 percent chance) or near normal (35 percent chance). More frequent and stronger-than-normal southwesterly quarter winds may shelter
- Soil moisture levels are most likely to be near normal (45 percent chance) while river flows are
(45 percent chance). Marine heatwave conditions remain present in coastal waters. The warmer
than average seas may reduce the intensity of cold, southerly air masses, especially near the
coast.
the region, leading to dry spells.
about equally likely to be below normal (40 percent chance) or near normal (35 percent chance).