"From Taupo northwards, we're going for heavy showers and thunder [today], but not quite so bad on Sunday," he said.
Severe weather warnings have been issued for areas including the Bay of Plenty, Taupo, Taranaki, Manawatu, Marlborough and Nelson.
A tropical low over the country means wet and humid weather will continue until about the middle of next week, Mr Gorman said.
Although the skies would be grey over the New Year weekend, temperatures would remain warm and humid, making for a hot and muggy couple of days.
"It won't be cold, so if you don't mind the rain you can still enjoy some swimming time at the beach."
A top temperature of 23C is forecast for Auckland today, and the first day of 2012 will also be hot, with a maximum of 24C.
Several holiday hot spots will be in for a soaking this weekend.
In Taupo, heavy rain - with the possibility of torrential downpours - is forecast, and the Bay of Plenty is also tipped to get heavy rain, with possible thunderstorms.
In the Nelson-Tasman region, heavy rain caused flooding and land slips in several areas, including Pohara, Motupipi and Golden Bay.
Other popular holiday areas, including the Coromandel and Gisborne, are also expected to get wet weather, particularly today.
In Gisborne, where the three-day Rhythm & Vines event finishes today, rain is expected to clear later in the day.
Mr Gorman said conditions in the South Island were only slightly better.
"You have to go down to Canterbury, Otago and the West Coast to have a dry start to the new year."
