Downpours are set to strike the lower South Island, with Fiordland and Southland under heavy rain watches.
MetService warned that the rainfall could approach warning criteria and there was a moderate chance of Southland's watch being upgraded to a warning.
The watches are in place from 9am today, with Fiordland about and north of Dusky Sound's watch ending at 9pm.
Southland is under a heavy rain watch until 7pm.
Much of the South Island's east coast, however, is set for a scorching Sunday, with temperatures almost reaching 30°C.
MetService said northwesterly winds and sunny conditions ahead of a cold front were driving the hot temperatures.
It said Blenheim was expected to reach 29°C, while Christchurch was forecast to hit 28°C, Timaru 25°C and Ashburton 27°C.
Further south, Dunedin was set to reach a high of just 19°C.
A cold front will see temperatures along the east coast dip on Monday.
