Weather: 'Westerly wind burst' to give atmosphere 'El Niño-like jolt', thunderstorms, strong wind on the way

Parts of the North Island could be in for some drier weather in February thanks to a "westerly wind burst" in the Pacific.   

The National Institute of Water and Atmospheric Research (NIWA) said on Thursday a unique phenomenon called a westerly wind burst (WWB) is unfolding in the equatorial Pacific.  

"This WWB will give the atmosphere an El Niño-like jolt heading into February," NIWA said. 

This will result in more westerly winds and drier conditions for the north and east of New Zealand.

MetService meteorologist James Millward told Newshub the WWB is being driven by a shorter-term driver called Madden-Julian Oscillation (MJO), which is essentially a tropical wave that moves around the equator.  

Millward said the MJO is set to change the weather patterns New Zealand has been seeing, resulting in the return of more high pressure in February, especially in the North Island.  

"So that would be sort of be more prolonged spells of settled weather. There's less room for those sorts of tropical systems to get down to New Zealand because the ridge is quite strong across the Tasman Sea and northern New Zealand," Millward explained. 

"Across the south of New Zealand, we typically see more... westerly winds and sort of more fast-moving frontal features coming through across sort of the West Coast of the South Island."  

Millward told Newshub New Zealand has had relatively wet weather across the North Island so far this summer, which he said is "slightly atypical" of what is expected from a normal El Niño summer. 

"But February is looking a little bit more typical in terms of what we would normally expect from a El Niño summer, with a drier signal for the North Island and wetter signal for the southwest of the of the South Island."

But while drier conditions are on the way for some regions over the course of February, MetService says a spate of bad weather is expected over the coming days.   

The forecasting agency has issued weather warnings and watches for the West Coast and lower North Island for Friday.  

An 'orange' heavy rain warning has been issued for the ranges of Buller from 9am to 7pm and the ranges of the Westland and Grey Districts from 4am to 4pm.   

MetService said these areas should expect 70-90mm of rain with possible thunderstorms at peak intensities of 20 to 30mm/h.   

"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous," MetService said. 

Strong winds are also set to lash Wellington and Wairarapa, including the Tararua District, from 1pm to 9pm on Friday, with an orange warning in place. 

MetService warns winds could reach up to 120km/h in exposed places.  

"Strong wind gusts could damage trees, powerlines and unsecured structures. Driving may be hazardous, especially for high-sided vehicles and motorcycles," MetService warned.  

A strong wind watch is also in place for the Marlborough Sounds and Canterbury headwaters north of the Rakaia River, while a heavy rain watch has been issued for Tasman west of Tākaka, including Nelson Lakes National Park.   

The strong wind warning has prompted Waka Kotahi NZ Transport Agency to issue a reminder for drivers to be prepared for the bad weather.   

Drivers must take special care on exposed routes such as SH2 Remutaka Hill and the Wainui Saddle on SH1 Transmission Gully, NZTA said. It particularly applies to motorcyclists, trucks, vans and towing vehicles.  

Drivers travelling on SH60 in Tākaka/Golden Bay and SH6 - Kawatiri to the West Coast - must be prepared for wet weather driving conditions.   

NZTA urges road users to drive to the conditions, watch out for hazards and allow for extra travel time.   

"The weather will coincide with afternoon peak travel times. Urban commuters and people heading away for the Waitangi Day holiday should drive accordingly – be ready for wind-blown debris and tree falls, increase your following distances, and use your headlights if visibility is poor," NZTA said. 

A MetService spokesperson told Newshub a strong cold front is working its way up the country from Thursday evening.   

Along with strong winds and heavy rain, the front will also bring a drop in temperatures.   

For the lower South Island, the temperatures will only be in the mid-to-high teens on Friday.   

The overnight lows will also be cold, with Queenstown and Alexandra only expecting five degrees on Saturday morning.  

Parts of the North Island are also expected to be hit by the cold temperatures. From the Central Plateau southwards on Saturday, temperatures may only reach the mid-to-high teens.  

Taumarunui is only expected to reach 17C on Saturday - eight degrees below average - while Taupō is thought to hit 17C, six degrees below average.