"That front will bring down some quite moist, sub-tropical air,'' she said.
Clark said this will bring a lot of rain for the upper North Island, particularly Northland and Auckland from about 9am today.
The biggest rainfall accumulations are expected over Northland, mainly about the eastern hills, and a Heavy Rain Warning is now in force, with peak rates of 10 to 20mm per hour expected from this evening, with possible localised downpours of 25 to 30mm per hour through the day.
The rain will extend into tomorrow and beyond, but will probably not be as heavy as today's precipitation, she said.
Clark said the downpours will probably leave the region's roads treacherous and people should take care while driving around the region.
The front will also bring gale-force winds to Northland, but the easterly winds are likely to have a greater impact on Auckland - which has a wind watch in place.
She said despite the heavy rain forecast, it's unlikely to end Northland's drought, ''though with some prolonged heavy rain, it will certainly help the situation up there".
The front will also bring some big swells of up to 2m along Northland's east coast today, growing to 3m later in the week.
Clark said people should stay up to date with the latest forecasts and warnings as the situation can change rapidly.
