MetService meteorologist John Law said Vaianu was currently a category 2 cyclone and it was continuing to move across the tropics.
It was forecast to head southwards and hit the North Island this weekend, bringing the potential for heavy rain and ‘‘damaging, potentially life-threatening’’ winds.
As it continues southward, off the east coast of the South Island, a strong front was expected to head up the coast, creating a ‘‘squeeze’’ between the two, which had the potential to lash the Otago coastline, and Otago Peninsula in particular, with very strong winds.
‘‘So, although at the moment our watches are for the North Island, we’re not quite out of the woods down on the South Island just yet,’’ Mr Law said.
‘‘As we head through, perhaps Sunday night, in towards Monday, and perhaps the first part of Tuesday, we’ll find some of those stronger winds down towards the Otago coast.’’
While it was still too early to say exactly how strong the winds might be, he said it was definitely worth keeping an eye on.
‘‘I think there’s still a fair bit of uncertainty about the exact path of Cyclone Vaianu and you can imagine that if this system is a little bit closer towards the Otago coast, you get that bigger squeeze — that bigger pressure difference — and we’ll find some stronger winds.
‘‘I think it’s one of those situations where we really need to keep a close eye on the forecast — particularly Sunday night and Monday morning, which is probably when it will be the windiest time through Dunedin, Port Chalmers and the Otago Peninsula.
‘‘There’s time for that to change and with this situation, it’s fast moving ... but it’s also a big broad system with impacts across many parts of New Zealand.’’
MetService has already issued severe weather watches.
Watches are normally issued one to three days ahead of a weather event, but Mr Law said the longer lead time of these watches was an indication of the event’s potential severity.
As confidence in the track of the cyclone increases, MetService would start issuing orange, or possibly red, warnings for heavy rain and/or severe gales.
