The humid conditions were being brought in by a flow of air off the northeast of the country, MetService said. A low-pressure system should replace this flow on Sunday but the sub-tropical air mass over New Zealand would linger.
While the northeasterly flow would continue to dump on the North Island on Friday, the National Institute of Water and Atmospheric Research said an “atmospheric river of moisture” would hit the West Coast of the South Island.
Auckland had showers forecast for Friday with another high of 27C. MetService predicted partly cloudy conditions with isolated showers in Wellington, where some northerlies could become strong in exposed places.
Christchurch had a 31C high forecast for Friday with cloudy periods and a few spots of rain expected for the morning. There was a chance of an early shower in Dunedin, where the forecast high was 28C.
Meanwhile, MetService has issued a raft of severe weather watches and warnings for the west of the South Island starting at 3am tomorrow.
An orange heavy rain warning is in effect for Westland, north of Haast, for 24 hours from 3am on Thursday as 180 to 220mm of rain is expected.
Peak rates of rainfall could reach 20 to 25mm/h, especially in thunderstorms, said MetService.
Heavy rain watches will also be in effect for Tasman about and west of Motueka, Buller, the headwaters of Otago lakes and rivers, Westland and south of Haast, and Fiordland throughout Thursday and Friday.
Niwa said the atmospheric river of moisture tracking into the West Coast of the South Island on Friday, may deliver up to a month’s worth of rain in a day to Westland, possibly causing flooding and slips.
Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.
A strong wind watch has also been issued for Fiordland for 13 hours from 6am on Friday.
