Most of North Island coastline at risk of flooding

Most of the North Island's coastline is at risk of flooding as a sub-tropical storm whips up ferocious seas combined with the biggest tides of the year.

Niwa is warning the approaching storm is bearing similarities to ex-Tropical Cyclone Ita, which struck at Easter three years ago inundating coastal communities across the upper North Island and blowing buildings to pieces on the South Island's West Coast.

Strong onshore winds meant king tides overnight Thursday and Friday posed a threat to many low-lying communities.

They included:
• all northward facing bays in Auckland
• Northland to Bay of Plenty, including Firth of Thames
• the North Island's west coast during midday high tide on Friday

MetService has now issued heavy rain and strong wind warnings for northern and central New Zealand for Thursday and Friday.

The storm, which is on track to hit the top of the North Island tomorrow, has winds so powerful they are expected to reach hurricane strength.

It is also expected to deliver a deluge of tropical-fuelled rain to many northern regions beginning in Northland and Auckland tomorrow.

Waves up to 7m high are expected to hammer North Island coastlines.

The storm is expected to sweep across the North Island before hitting northern and eastern regions of the South Island.

MetService says heavy rain warnings are likely for Coromandel Peninsula, Bay of Plenty and the western ranges of Gisborne when the storm hits late Thursday.

Weatherwatch.co.nz head analyst Philip Duncan said the storm would rapidly deepen and intensify before it made landfall tomorrow.

Campers and trampers were warned to be aware of the deteriorating conditions.

Duncan said models showed the storm was expected to peak early Friday. A wind map put the worst of the winds becoming hurricane force - 120 km/h - for a time at the centre, although such winds would stay mainly out at sea.

MetService says severe gales will buffet the upper North Island from Taranaki to Bay of Plenty north.

The heaviest rain is expected in Northland, Auckland, Coromandel Peninsula, Bay of Plenty, Mt Taranaki, Marlborough and Nelson.

MetService is warning the combination of strong winds and high tides could cause coastal inundation about eastern areas from Northland to Bay of Plenty including the Firth of Thames.

Northern Coastguard operations manager Ray Burge today urged boaties to keep an ear on the marine forecast in coming days.

Given the dreadful forecast boaties were advised to consider returning home early or go to a safe harbour to sit out the coming storm.

Burge said the big tides threatened to amplify the effect the storm had on coastal communities. He said the indications were the storm would be ferocious but pass quickly.

He advised boaties to stay ashore if the weather was marginal and to not put themselves at risk securing their vessels.

It is expected to clear the country on Saturday.