The lowest maximum temperatures have been forecast in Waiouru, Greymouth and Hokitika, which are expected to get to 20C.
A northwest flow will strengthen over the South Island on Monday before a front that approaches from the Tasman Sea.
The front briefly moves onto the far south on Tuesday morning before being pushed back southwards by the strong ridge.
There is a small chance rain will reach warning criteria about Fiordland from Monday evening to Tuesday evening, and northwest gales about exposed parts of Fiordland, Southland and Stewart Island may become severe for a time on Monday and Tuesday morning.
The ridge of high pressure then moves east of the county on Wednesday, allowing a northerly flow to spread over all of New Zealand.
The northerly flow strengthens on Thursday before another front that approaches the country from the west.
Be prepared for traffic chaos in Auckland
As more than 30,000 people descend on Auckland's waterfront for the Ports of Auckland Round the Bays event today, city goers should expect increasing traffic and nightmarish parking.
The 8.4km annual fun run starts from Quay St, goes along Tamaki Drive and finishes at Vellenoweth Green, St Heliers.
Guess what day it is 🤭 IT’S RACE DAY!!
We can’t wait to see your teams in the fitgear you’ve had laid out for weeks...
Posted by Round the Bays on Saturday, 2 March 2019
Many of the surrounding roads will be closed from 6.30am until 12.45pm, including parts of Customs St, Market Ln, Lower Hobson, Quay St, Tamaki Dr, Ngapipi Rd, Long Dr, Auckland Rd, The Parade, Goldie St, Maheke St, Benbow St and Polygon Rd.
Auckland Transport advises participants taking public transport to the event to plan travel in advance and allow extra time.
Buses will operate to their normal Sunday timetable, but because of road closures on Quay St and Tamaki Dr, some bus services will be diverted during the event.
There is a free shuttle running between the start and finish line.
Because of scheduled maintenance on the Southern and Eastern train lines, some trains have been replaced by buses, but western line services are operating as normal.
Southern line trains are operating between Britomart and Penrose, and buses have replaced trains between Penrose and Pukekohe.
Eastern line trains are operating between Britomart and Sylvia Park, and buses have replaced trains between Panmure and Manukau.
Ferry services are running as normal.