Heavy rain is forecast for the Bay of Plenty as an active trough moves up the country.

An active trough, which is bringing heavy rain to central New Zealand, is expected to move slowly north-eastwards over the North Island during Friday and has seen a severe weather warning issued.

Bursts of heavy rain are expected on Friday. Photo: File.

The heaviest falls are likely about the Tararua Range, Taranaki, Waitomo, Taumarunui, Tongariro National Park and the ranges of the Eastern Bay of Plenty.

'Accumulations may reach 120 to 150mm in a 12-to-18 hour period, especially about the ranges,” says a statement from the MetService.

'Another weaker trough is expected to weaken as it moves over the South Island during Friday.”

In the Eastern Bay of Plenty, rain was expected to set in on Thursday evening and become heavy overnight, before easing on Friday evening.

In the 18 hours from 12am to 6pm Friday, 120 to 180mm was expected to accumulate.

'A strong and very moist north-west flow was responsible for this extreme weather, and is now moving onto the North Island, with many areas likely to be affected by heavy rain and severe gales,” says meteorologist Peter Little.

'In addition, a watch is in force for a burst of heavy rain over the upper North Island including Auckland for Friday morning.

'A disturbed north-west flow persists over much of the country through to the middle of next week.

'The only respite is a ridge that moves eastwards across northern New Zealand over the weekend, which is good news for those wanting to enjoy Mothers' Day outdoors.

'We are expecting fine weather over northern and eastern parts of the country over the weekend.

'After a fine day on Saturday, the south-west of the North Island will likely see increasing cloud and wind for Mothers' Day.

'Unfortunately, folk on the West Coast can expect unsettled weather to prevail, so it would be advisable to plan for indoor activities with Mum.”