Mr Duncan said the tropical low was expected to head towards the east of Northland, over the East Cape and into the Bay of Plenty, where heavy rain caused flooding, slips and road damage this week.
Rain is expected to peak between Sunday and next Tuesday, before another tropical low is forecast to head to the West Coast on Thursday and over the North Island by Friday.
In Auckland, showers and light rain are expected over the weekend with temperature highs of 23C and lows of about 17C.
Next week will bring seven days of rain, with the average temperature high of about 24C.
The muggy weather that many parts of the country felt just before and after New Year is also back.
"In between these rain events will be plenty of cloud and humidity," Mr Duncan said.
Meanwhile, last month's horrible weather just before Christmas brought some record lows, said Niwa.
On December 20 Auckland experienced a record low of 11.7C, while December 9 proved to a muggy day in the city with a record high of 24C.
Mr Duncan said Kiwis should look forward to the coming months.
"Keep in mind that February and March are often very settled ... there will be many New Zealanders praying for that to happen."