There will be increasing cloud and strong northerlies in Wellington, and the daytime high of 22C will fall to 15C overnight.
Holiday hotspots are also looking good.
In Northland, where the three-day Northern Bass festival at Mangawhai concludes early New Year's Day, light winds, sunshine and temperatures in the mid to high 20s are expected.
Party-goers at the perennially popular Rhythm and Vines near Gisborne can expect similar conditions, as can those enjoying a lake escape in Taupo or beach time in Coromandel Peninsula.
Fine in north and east, wet in south
In the South Island, northern and eastern areas can expect a fine, warm day tomorrow.
A high of 27C in Christchurch will dip to 13C overnight, and Blenheim and Nelson also forecast to heat up to highs in the low to mid 20s, falling to the mid-teens overnight.
The forecast is less positive in the south.
Dunedin's 22C daytime high will drop to 10C overnight and there may be a few showers.
Rain is expected in Southland and up the West Coast, and revellers in Queenstown will need to pack a jacket, with a low of 10C overnight and a southerly change bringing some rain in the evening.
The first day of 2018 should dawn fine for most, although farmers in parts of Taranaki will be smiling with rain expected.
And there could be more for the rest of us.
A low coming down from the north of the country could bring "decent rainfall" to some areas, Murray said.
"Depending on where it tracks it could bring quite significant rainfall on Thursday or Friday. We're keeping a very close eye on that."
More would be known by Tuesday, she said.
Meanwhile, roads were late this week congested with holidaymakers travelling to destinations far and wide, as New Year's Eve approached.
Seven people have died on New Zealand roads since the holiday period began, among them two men killed in head-on smash in South Canterbury on Boxing Day.
They were named yesterday as Horton James Hill, 80, of Christchurch, and 31-year-old Matthew James Gilchrist, of Oamaru.
New Year's Eve weather
Whangarei: Fine, 26C
Auckland: Fine, 24C
Hamilton: Fine, 24C
Tauranga: Fine, 26C
Taupo: Fine, 23C
Wellington: Becoming cloudy in the afternoon, 20C
Christchurch: Increasing high cloud, 27C
Dunedin: Occasional rain in morning, easing evening, 21C
Queenstown:Occasional rain, easing evening, 20C