Dozens of flights in and out of Christchurch have been cancelled due to low visibility and fog - which may return tomorrow - while parts of the North Island prepare for heavy rain and thunderstorms as a bleak Saturday unfolds across the top half of the North Island.  

The fog has now cleared, but not before more than 40 flights were either diverted, turned back, delayed or - in the case of seven outbound and five inbound flights - cancelled, an Air New Zealand spokeswoman said.  

Customers were being rebooked, and those travelling to and from Christchurch should keep an eye on the airline’s app and the arrivals and departures page on their website for up-to-date information. 

Fog disrupted dozens of flights in and out of Christchurch Airport this morning, and may again tomorrow. Photo / NZME 

Meanwhile, heavy rain and thunderstorms are forecast in the upper North Island today as a shallow low moves onto the island from the north Tasman Sea. 

MetService have issued orange alert level heavy rain warnings for Bay of Plenty, about and west of the Rotorua area, until 7pm. 

In Bay of Plenty east of the Rotorua area, the orange heavy rain warning is in place from 4pm to midnight. 

“Expect 60 to 80 mm of rain in parts of the region. Brief peaks rates of 25 to 40 mm/h likely in localised downpours, with thunderstorms also possible.” 

Heavy rain watches, with possible downpours and thunderstorms, have also been issued for Northland until 2pm, Auckland, Coromandel Peninsula and Waikato until 6pm, and Gisborne/Tairāwhiti from 3pm today until 2am tomorrow. 

“Amounts may approach warning criteria and may even exceed warning amounts in localised areas, especially north of Tolaga Bay.” 

The thunderstorm risk was moderate for Northland and northern Auckland (including Hauraki Gulf) early this afternoon, Coromandel Peninsula and western Bay of Plenty this afternoon and evening, and in eastern Bay of Plenty and northern parts of Gisborne/Tairāwhiti this evening. 

For anyone in the upper North Island who is reading nzherald.co.nz before looking outside, it’s raining today. 

“Things will be grim for the upper half [of the island] but things are looking better tomorrow”, MetService meteorologist Alwin Bakker said. 

“The low affecting the North Island will be moving away to the east, just getting the tail end of it … with showers. The chance of a shower will be higher in the east.”  

Aucklanders can expect isolated showers, which become widespread and possibly heavy for a time late in the morning and afternoon, and a high of 19C tomorrow, while it would be cloudy with the chance of a shower until afternoon and a high of 20C in Hamilton.  

The capital would be mainly fine with a few spots of rain and a high of 17C.  

And while drier, the South Island was being chilled by a series of weak cold fronts today, but would also see an improvement in its weather from tomorrow.  

An overnight low of 7C and high of 18C was expected in the Garden City tomorrow, but fog may again cause headaches for air travellers with low cloud of fog clearing from late morning.  

Dunedin would be mostly cloudy with occasional rain before dawn and in the evening, and a high of 16C. 

And while most of us are back to work on Monday, families enjoying the second week of school holidays could look forward to more settled weather, Bakker said. 

The anglers at Auckland's Cornwallis and elsewhere might have better luck with the weather tomorrow, as breaks in the rain increase across the country. Photo / NZME 

Temperatures would remain mild, with highs around 20C across most of the top half of the North Island and the top of the South Island, and in the mid to late teens elsewhere. 

It was looking “quite nice everywhere” on Monday, he said. 

“There’s a big ridge of high pressure across the whole country. There’ll still likely be some showers about, but it’s generally looking nicer than today.” 

Cherie Howie is an Auckland-based reporter who joined the Herald in 2011. She has been a journalist for more than 20 years and specialises in general news and features. 

This article was originally posted on the NZ Herald here.