Police say caution is required on SH1 between Warkworth and Wellsford.
"Heavy rain in the area has caused damage to the road surface, so motorists are asked to slow down and drive to the conditions," they said in a statement.
Anyone holidaying in the Coromandel Peninsula can expect a further 100mm to 130mm of rain to accumulate on what has already fallen - with peak rates of 20mm to 25mm an hour expected early this morning and afternoon.
Up to 130mm of rain is forecast over Gisborne, north of Tolaga Bay, and the eastern ranges of the Bay of Plenty. People there are also being urged to keep an eye on updates throughout the day.
Northland - especially in the eastern ranges - was expected to get a further 70mm to 90mm by early this morning.
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In Auckland, especially north of the city, a heavy rain watch remains in place until later this morning. The same rain watches are in place for Great Barrier Island and the Hunua Range, south of the city.
Periods of heavy rain are expected in the City of Sails this morning, with rainfall amounts potentially approaching "warning criteria", MetService said.
Auckland has a temperature high of 19C and overnight low of 14C. By 8am, the temperature was feeling like "three layers of clothing" outside and gusts of up to 41km/h are on the cards too.
Weather authorities also have a strong wind watch in place for Northland, Auckland and Coromandel Peninsula, Waikato, Gisborne, Bay of Plenty and Rotorua.
Fine in the south
Meanwhile, those in the South Island can expect a generally fine day - save for high cloud and patchy rain expected from this afternoon in Nelson, Marlborough and northern Canterbury.
Christchurch has a high of 15C and overnight low of 6C and those in Dunedin will see beautiful conditions and a high of 16C.
