Saturday night may be best spent inside, with thunderstorms and rain expected in many parts of the country.
Lightning, thunder and rain are already being seen in Wellington this evening.
MetService is warning that Waikato, Bay of Plenty, the Gisborne ranges, Taranaki, Manawatu and the Kapiti Coast, as well as the capital, are all at risk of thunderstorms.
The already-soaked Buller area and the Nelson ranges may also see thunderstorms and more heavy rain tonight.
And Dunedin and Clutha are in line for steady rainfall between now and tomorrow morning.
A MetService duty forecaster said a low pressure system is to blame for the unstable conditions.
She said the system has come in behind the front that brought heavy rain to parts of New Zealand yesterday and today.
Earlier, heavy rain in Wellington prompted a police warning to motorists with widespread surface flooding in the Wellington area this afternoon.