After three days of record high temperatures in parts of Southland and Otago, rain is expected to arrive in the lower South Island regions today.
Invercargill - the country's southernmost city - beat a 100-year old record for its hottest day on Sunday, with the temperature reaching 32.3°C.
Dunedin Airport also set new a record for its highest recorded temperature yesterday, when the mercury hit 35°.
That intense hot spell is set to end today, with scattered rain and temperatures in the low 20s forecast for Otago and Southland.
There is also the possibility of thunderstorms in Southland.
Warnings are also in place across Northland, Auckland, Taranaki, Nelson and Marlborough as well as the ranges of Westland.
Flooding has started affecting the top of the South Island, and the Transport Agency warned drivers using State Highway 60 between Takaka and Collingwood were asked to take extra care.
A spokesperson said a temporary speed restriction was in place near Little Onahau River Bridge because of flooding.
MetService meteorologist Lisa Murray said the slow-moving front may cause surface flooding and slips, but would offer a reprieve for some areas.
"There's quite a lot of dry areas still around the country and some of those are the northern parts of Westland, the coastal Buller area and some parts of Nelson and Taranaki as well. And those areas are all going to see some decent accumulations during this event."
A heavy rain watch is also in place for the recent flood-hit Coromandel and Ms Murray said people needed to keep an eye on forecasts in case things change.
MetService said the heavy rain moving up the country is expected to reach Auckland later in the week, with up to 120mm of rain possible between 6am and 6pm tomorrow.
Meanwhile, in Auckland, Gulf Habour ferry services have been affected by high winds and will be operated by bus until further notice.