Boxing Day thunderstorms are possible in many areas of the North Island and northern South Island, but a threat of widespread heavy rain has eased.
Localised heavy rainfall was possible, and over inland parts of Marlborough, Nelson and Buller rainfall rates could approach 40mm an hour in some places, MetService said.
More widespread heavy rain was unlikely, and a severe weather watch for possible heavy rain over a wide area had been lifted.
"Hot and humid conditions continue over North Island while a cooler change is moving northwards over the South Island."
The low that was formerly Tropical Cyclone Evan should move slowly onto the central North Island this afternoon and evening, with scattered showers and continued hot humid conditions.
The cooler southerly wind change should spread onto the southern North Island.
Thunderstorms were most likely about the southern North Island from Taihape and Hawke's Bay to southern Wairarapa, and also about inland parts of Marlborough, Nelson and Buller.
A broader low risk of thunderstorms covered the area from Waikato to about Wanaka as indicated on the chart, MetService said.
Christmas Day temperatures:
Auckland: 24.6 degrees at the airport
Hamilton: 26.2 degrees at the airport
Tauranga: 23.4 degrees at the airport
Wellington: 29.6 degrees at the airport, 32 degrees in Lower Hutt
Christchurch: 22.6 degrees at the airport
Dunedin: 21.4 degrees in the city, 27.1 degrees at the airport