Most of the South was bathed in brilliant sunshine at the weekend, particularly in Alexandra, which recorded a high of 26°C on Saturday, with most of the rest of the region in the early 20s.
Dunedin city reached a high of 23°C on Saturday.
MetService forecaster Oscar Shiviti said the settled weather should continue for a few more days.
"We're having a high pressure system that's building in from the Tasman Sea, so that's slowly pushing up New Zealand.
"We're actually expecting this type of conditions to persist for much of the week. So for a lot of the areas in the South Island, we're expecting significantly higher temperatures."
Mr Shiviti forecast temperatures to reach a high of 29°C in Alexandra and Wanaka today, and 25°C in Dunedin today.
Temperatures in the South should be similar tomorrow, and "fairly consistent" until Waitangi Day, he said.
"You'll see a change on Waitangi Day. We are expecting a front to start moving up the South Island, but it's going to start in the southern part. So that's the reason for the temperatures dropping sharply on Thursday."
