Twenty-four hours of heavy rain is looming for the top half of the North Island with forecasters particularly concerned for Bay of Plenty.

Orange heavy rain warnings lasting around 24 hours are in place for Coromandel Peninsula from 2pm, Bay of Plenty from 8pm, Tongariro National Park from 10pm and Gisborne/Tairāwhiti, north of Ruatoria from midnight.

Severe thunderstorm watches were also in place for Bay of Plenty and Rotorua until 3pm today.

“Streams and rivers may rise rapidly. Surface flooding, slips, and difficult driving conditions possible,” MetService warned.

Earth Sciences New Zealand (formerly Niwa) forecaster Chester Lampkin told the Herald this morning that an area of low pressure in the Tasman Sea and a cold front coming in from the southwest would bring a big plume of moisture from the Tasman.

As well as heavy rain for many, warm nights could also be expected.

“We call it an atmospheric river because the amount of moisture coming with it,” Lampkin said.

“There is an area of high pressure to the east that is blocking the weather pattern, where it slows the weather down to almost a standstill, which makes the storms move a little bit slower.”

MetService forecaster Alec Holden told the Herald a lot of rain was spread across the North Island.

Up to 120mm of rain was expected in Gisborne/Tairāwhiti, 180mm in Coromandel Peninsula and up to 200mm in Bay of Plenty, with localised downpours of 25 to 40mm/h possible, the largest accumulations likely west of Whakatāne.

Forecasters were most concerned about Bay of Plenty, Holden said.

“There is a moderate chance Bay of Plenty gets upgraded to a red warning in terms of rainfall.”

The agency encouraged people to clear their drains and gutters, avoid low-lying areas and drive cautiously.