Heavy rain is lashing parts of the country today with some places under heavy rainfall warnings already measuring more than 100 millimetres of rainfall in the past 24 hours.
A deep slow-moving low to the west of the North Island was directing a strengthening east to northeast flow over the country, and MetService said some places already being battered by rain could expect another 24 hours of solid rainfall.
In the Coromandel, eastern ranges of Waikato, Bay of Plenty and northern Gisborne, heavy rain would not clear until at least this afternoon, with up to 120mm of rain possible, MetService said in a severe weather warning.
In the Coromandel Peninsula, more than 100ml had already fallen, 96ml in the Takaka Hills and about 100ml in the Nelson Ranges.
In populated areas, Whitianga has had the biggest rainfall so far with 50ml.
In Nelson and Marlborough, up to 120mm of heavy rain was expected from early today through until about midnight.
Rain was expected to become heavy around midday today in eastern areas of Canterbury and Otago from the Rangitata River to Clutha district.
South of Palmerston, the rain was expected to ease by midnight, but further north it was likely to remain heavy until tomorrow evening. Up to 150mm of rain could fall about the hill country of South Canterbury and North Otago, while further south 70mm was possible.
People in the affected areas were are advised to be aware of river levels and watch for localised surface flooding and slips, MetService said.
Heavy rain that had been affecting southern Fiordland should ease this morning, but southeasterlies were forecast to rise to severe gale in exposed parts of the area this afternoon with gusts of around 130kmh in exposed places, especially along the fiords. The winds should ease during tomorrow morning.
Winds of that strength could damage trees and powerlines, MetService said.
Snow was expected down to 500 metres in Southland this afternoon.
In Northland and Auckland westerlies were expected to rise to gale for a time today, while gale northeasterlies in Coromandel, Waikato and Bay of Plenty were expected to change to lighter northwest winds this afternoon.
Waikato Regional Council said the rain could place further pressure on already swollen rivers.
The Piako and Waitoa Rivers could return to levels seen earlier last week, while the Waihou could also come under pressure.
Emergency management officer Greg Ryan said forecasting suggested the river systems and the council's flood management infrastructure should be able to cope with any new downpours.
"But farmers and the general public need to be aware of the potential for rising river levels, slips and difficult road conditions."
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