MetService warns New Zealand is at risk from "slow-moving" thunderstorms and downpours on Saturday.
"The combination of another warm humid day with light winds is expected to allow daytime cloud buildups to produce scattered heavy showers and a few thunderstorms about the central North Island and possibly the upper South Island this afternoon and evening," MetService warns.
"Any thunderstorms that develop today will be accompanied by localised heavy rain of 10-25mm/hr and possibly small hail.
"As the thunderstorms will be slow-moving, there is also a low risk of a few localised downpours of 25-40mm/hr, which could cause surface flooding and make driving conditions hazardous."
On Sunday, a rain-band in the Tasman Sea will approach the southern South Island, with rain spreading into Fiordland and southern Westland during the morning.
MetService says severe weather watches and warnings for wind and rain have been issued for parts of central and southern New Zealand.
"There is a moderate risk of thunderstorms embedded within this rain-band over central and southern Fiordland from late morning."
Over the second half on Sunday, the front moves slowly northwards over the southern South Island.
"Heavy rain is expected about Westland and Fiordland, with northwest gales about central and southern New Zealand," MetService says.
"There is a moderate risk of thunderstorms embedded within this rain-band about Fiordland and southern Westland, and also just east of the main divide, during Sunday afternoon."
