A weather "tempest" set to sweep across the North Island on Saturday could be damaging and dangerous, forecasters warn.
Metservice said a deep and vigorous low is expected to pass quickly across the North Island on Saturday morning.
Its statement described the weather system as a "tempest".
Meteorologist Daniel Corbett said the low would bring gales which could be severe and damaging in some areas.
Large waves were forecast on the west coast from Taranaki northwards, and on the east coast from East Cape southwards, he said.
"In short, this is a serious situation and poses a weather hazard for many North Island places."
Heavy rain was also likely in some North Island places on Saturday, while daytime temperatures were expected to be low, Mr Corbett said.
"This is a recipe for cold driving rain. Those who are out and about on Saturday are likely to describe the conditions with words like 'miserable' or 'atrocious'."
Weatherwatch.co.nz forecaster Philip Duncan said the low met the criteria of a "weather bomb".
Air pressure was set to plummet in a 24 hour period - much faster than the usual rate for a storm to develop, he said.
"It will go from a non-existent mark on our weather maps today to a nasty storm by Saturday morning."
Mr Duncan said the gales force winds brought to many parts of the North Island by the storm would be destructive in extreme cases.
Winds would come from all directions, with a period of heavy rain at the beginning of the low, he said.
Metservice advised boaties to check their moorings and secure loose objects on Friday in preparation for the system moving in on Saturday.
- HERALD ONLINE