Duncan expected winds as strong as 120 to 130 km/h to hit Northland and possibly northern parts of Auckland before it calmed down today.
The two lows will join up, forming a complicated weather system bringing heavy showers and strong winds to many, but leaving other parts of New Zealand bathed in sunshine.
The places to be today include Bay of Plenty, Gisborne and Hawke's Bay.
Southwesterlies will bring heavy showers and strong gusts to the northern North Island, although there will be fine spells too, Mr Duncan said.
Further down the country, a dusting of snow on Mt Ruapehu was the first sign of winter's arrival.