Rain could also develop in the lower North Island, with a high of 19C predicted for Wellington.
There was a chance the weather would clear in the lower North Island by midnight, Ms Ranger said.
There would be short periods of rain in the east of the South Island, but it was likely to be a mostly fine day.
"Those on the west of the South Island should get heavy rain, but that will ease to showers."
Weatherwatch analyst Philip Duncan predicted the driest places to be this New Year's Eve were Gisborne, northern Hawkes Bay, Coromandel and South Canterbury.
Those areas with the highest risk of rain were Taranaki, Wanganui, Manawatu, Nelson, the West Coast and Waikato.
Christchurch and Dunedin would have a warmer, drier day although there was a chance of very light rain in Christchurch in the afternoon, Mr Duncan said.
It would be mainly fine throughout the North Island in the morning, before late afternoon rain would hit Taranaki and Wellington first, and then Manawatu and Wanganui, before the rain travelled eastwards into Northland and Auckland later that evening.
Looking ahead to the first day of 2015, showers are expected for the northern parts of the North Island, however elsewhere it is expected to be mainly fine.