Storm set to bring 5m swells and rain

Watch out for coastal weather conditions like the seas that pounded Paihia in April 2013. Photo/Peter de Graaf

People on Northland's east coast are being urged to batten down the hatches ahead of a tropical storm later this week, due to bring winds up to 55 knots (102km/h) and 5-metre swells.

High swells along the east coast on Friday will precede heavy rain on Saturday, which may provide some relief for Kaipara farmers fearing another drought.

MetService meteorologist Daniel Corbett said a large, slow-moving anticyclone should bring mostly fine, settled weather to much of New Zealand today and tomorrow, but things will start to turn nasty late on Friday. Compounding the situation is the possibility of a second cyclone coming into the picture. Whangarei Coastguard boss Dave Grey is warning boaties to secure their vessels as soon as possible, rather than wait until the big storm hits. "I'm advising people not to leave it until the end of the week.

"Boaties should ensure their vessels are moored securely and, if they're up on a hard stand, properly tied down," Mr Grey said.

The storm is due to make its presence felt from Thursday but its high point will be on Sunday.

"Starting Thursday, we're looking at 15-10 knot easterlies, on Friday we're looking at 25 through to 40 knots south to southwesterly winds, and on Saturday, 30 through to 45 knots, south to southwesterly.

"But on Sunday we're looking at 45 to 55 knots, when the centre is over us.

"The wind will change from southeast to southwest, then to northwest. It will be rough," Mr Grey said.

"People need to be aware this is early days yet but it's on the cards these three fronts will combine to form one big one, he said."

Mr Grey said the conditions would whip up Whangarei Harbour.

People on the coast should treat it much like a tsunami warning and stay away from low-lying areas.

All coastguard units on the North Island's east coast were being briefed about the impending storm, Mr Grey said.

Even if the expected force does not eventuate, the situation would involve severe winds, high tide surges, heavy rain and low barometric pressure.

"It has the potential to affect everyone but we absolutely have to get the message out to boat owners: secure your vessel."

Mr Corbett said heavy rain on Saturday would be preceded by huge seas along Northland's east coast.

"It will be like when you pound your fist in the bath tub and all the water swells up around it.

"That will be your east coast on Friday, so anybody planning to go out on the water then or over the weekend really needs to keep an eye on what the sea is doing," Mr Corbett said.

"It's not going to be too flash on Saturday, so you should enjoy the fine weather while it lasts."

He said the low pressure system should bring a band of heavy rain across Northland on Saturday.

"While most people won't be too happy to see that much rain, it could provide some welcome relief to those [Kaipara] farmers who are getting very dry," he said.

"You are going to get a good slug of rain but we won't know exactly how much until later in the week, once it is known what the tropical weather systems were doing."

Tropical cyclone Hadi in the Coral Sea is expected to stay in the tropics for the time being but a new tropical low near Vanuatu is likely to become a tropical cyclone in the next day or so, before taking a path leading out of the tropics.

He said in the meantime people could keep an eye on developments with Fiji metservice at www.met.gov.fj, MetService TV and at www.metservice.com/warnings/severe-weather-outlook.

People could also follow updates @metservice on Twitter and MetService New Zealand on Facebook.