Cyclone Donna's remnants will hit off the coast of Kaitaia at midnight on Thursday and will take another day to travel down to the Gisborne area.
The closer it gets to New Zealand the more steam will be clipped from Donna's wings because of increasing wind in the area, sullying its "rotational energy".
However, although there will be some strong northerlies on the coast, they will not be cyclone-strength.
The storm was also travelling with "high top clouds", he said, a thick, expansive area of cloud in the atmosphere, which will create heavy, soppy rain, or thicker, heavier, droplets.
"You're not going to feel little droplets, this will bring soppy, heavy rain conditions. Once the rain sets in, it's in there."
The rain will begin tomorrow and continue into Friday and the weekend.
A severe weather warning was issued by MetService at 10am for heavy rain across central parts of the country.
"A period of northerly rain is expected over much of central and northern New Zealand," it said, ahead of a front expected to move in tomorrow.
The heaviest rain is forecast for Nelson, Mt Taranaki and parts of the Bay of Plenty, as well as the ranges of Gisborne.
Meanwhile, Weatherwatch said Donna is likely to weaken as it drifts south from the warm air and seas of the tropical south Pacific, but then restructure into a new system in the New Zealand area.
The remnants from Topical Cyclone Donna would just miss the country, it said, tracking to the north-east of the North Island. However, it warned that a change of course was always possible.
"If there wasn't a large blocking high to the east of New Zealand WeatherWatch.co.nz believes Donna would pose no threat to New Zealand, and quickly track well to the north-east.
"The high, however, is encouraging Donna to track closer to Aotearoa and therefore it brings a general threat; such as heavy rain, gales and dangerous beach conditions in the north-east of the North Island."
