There is a risk of thunderstorms today and tomorrow on the west of the South Island. Thunderstorms are also expected to pass through Kapiti today.
"In places like Fiordland and lower Westland they'll be seeing intermittent, isolated thunderstorms, and their could be some good gusts with that and hail," Clark said.
"But again, no-one should really be out and about in Fiordland so most people won't see the worst of it."
Temperatures are expected to fall across the South Island. Inland places like Alexandra could wake to frosts tomorrow morning. Overnight temperatures will fall as low as 3C.
The North Island is expected to be warmer - about 20C in Auckland - and showers will ease today.
"It will actually be fairly dry right into tomorrow," Clark said. "It is just western areas in the North Island that could get showers."
That weather pattern is likely to continue tomorrow, with mostly dry weather in the North Island, and temperatures in the low 20s in Auckland.
Showers are again expected in the west of the island, while the East Coast is expected to be fine.
Strong wind warnings are in place for the Canterbury high country, parts of Marlborough and the Wellington and Wairarapa regions tomorrow.