Tropical storm closes in on NZ

File photo / Alan Gibson

A severe tropical storm is closing in on New Zealand, with some forecasters predicting it will hit the country with cyclone-strength winds and rain.

Weatherwatch.co.nz head analyst Philip Duncan said Cyclone Wilma had not weakened into a subtropical low as fast as expected and could pass over Cape Reinga as a category 1 or 2 tropical cyclone.

It would bring far more severe weather than the remnants of two tropical cyclones - Zelia and Vania - that hit New Zealand earlier this month, he said.

"Tropical Cyclone Wilma will be far more serious than Zelia or Vania but much faster moving.

"The cyclone is likely to be a weak category 2 or strong category 1 cyclone when it passes Cape Reinga around midnight tonight."

The impending weather has put a halt to some Fullers Ferries between Auckland and Great Barrier Island.

The 6pm sailing tonight and tomorrow morning's ferry have both been cancelled.

The MetService said winds would be severe for a time overnight around Great Barrier Island, where gusts of 130km per hour were possible, which could damage trees and power lines.

Auckland Civil Defence is urging people to check drains and spouting at home and clear any blockages, as well as pick up debris that could become airborne.

MetService has predicted Cyclone Wilma will bring exceptionally strong winds and possible flooding as it moves past the country.

It has issued severe rain warnings for Auckland, eastern Waikato, Coromandel Peninsula, Bay of Plenty and Gisborne for tomorrow morning, saying slips or flooding are possible.

The cyclone has already caused widespread damage in Samoa and Tonga, where it knocked buildings down and blew over trees.

"It should sideswipe the northeastern parts of Northland on Saturday morning, then get pushed off to the southeast and sideswipe Gisborne on Sunday evening. Then it will move way off to the east of us," said MetService weather ambassador Bob McDavitt.

MetService says when Wilma passes by New Zealand, it will no longer be a tropical cyclone, but will bring strong winds and heavy rain to parts of the North Island.

The heaviest rainfall is expected in Northland where 150mm to 200mm may fall within 24 hours, with rainfall rates possibly reaching 25 to 50mm per hour, which could cause surface or flash flooding, lead to slips and cause rivers and streams to rise quickly.

The rain would be accompanied by strong or gale force winds.

Northland already received 240mm of rain in 30 hours last weekend - more than double the region's average monthly rainfall of about 105mm.

Northland Regional Council civil defence manager Graeme MacDonald said he expects the storm to peak with rainfall of 30mm/hr in the early hours of Saturday.

"Once again, that will mean parts of the region could see surface flooding as rivers rise quickly."

"The rain is also expected to be accompanied by strong or gale force winds, particularly for exposed parts of the region and forecasters are also predicting heavy northeast swells and very rough seas for eastern coastal areas."

Mr Duncan said the cyclone would not affect the temperature and he has forecast between 24C and 26C for most of the upper North Island.

"The humidity may increase a little bit, but it won't get as bad as we've had recently."

Mr Duncan said the severe wind and rain would move off the country quickly with the promise of clear weather on Sunday and Monday.

"It's a quite a fast-moving weather system."

Environment Waikato emergency management officer Adam Munro says localised flooding is expected as rivers are still high after heavy rain last week.

He says the region doesn't have the cushion it had last week given it experienced a dry spell before the rain.

But Adam Munro says the good news is that expected rainfall figures aren't as high as last weekend.

- with NZPA