"Uncomfortably muggy" nights are coming for New Zealand as warm humid air is dragged down from the tropics, pushing temperatures up.
"A northerly quarter flow of air (NE to NW) will be the theme over the next several days, resulting in above-average temperatures for many areas," NIWA says.
This could drive some eastern South Island locations to 25C on Sunday, with even warmer temperatures to come after this.
"In fact, from Gisborne to the Wairarapa, widespread mid-20s are possible by the middle portion of next week," NIWA adds.
MetService says uncomfortable nights could continue for the North Island through until at least Thursday.
On Monday a weak front will move slowly eastwards over the central North Island with scattered rain or showers.
"During the afternoon and evening, there is a low risk of a few thunderstorms developing about inland areas from Waikato to the Whanganui hill country and across to central and southern Hawke's Bay," MetService says.
"If any thunderstorms do develop, they will bring localised heavy rain."
On Thursday and Friday, there is a low confidence of rainfall accumulations meeting warning criteria over large parts of the North Island.
"It looks possible that Bay of Plenty and Gisborne ranges could be upgraded to moderate confidence on Friday, but as it is the last day of the outlook period it is too soon to say," MetService adds.
