Metservice has upgraded the severe weather watch placed over central New Zealand to a warning.
Issued this morning, the warning predicts significant heavy rain and severe north-west gales will hit in the late afternoon.
The weather bomb has been attributed to a rapidly deepening low and associated front over the Tasman Sea.
“This significant low and frontal system are preceded by a very strong and moist northwesterly flow, bringing heavy rain to western parts of central New Zealand and north-west gales to much of the country.”
While the heaviest rain is expected to fall over Westland, the ranges of north-west Nelson, Nelson Lakes and Buller are set to be drenched by 100 to 180mm of rain within a 15-18 hour period from Wednesday afternoon into Thursday morning.
“This amount of rain will cause rivers and streams to rise rapidly, surface flooding and possibly slips.”
The rainfall is expected to reach peak intensities of 20 to 30mm per hour from Wednesday night, with possible thunderstorms.
Severe north to north-west gales is set to accompany the heavy rain in exposed places across Nelson and Buller.
Meanwhile, Wairarapa, Wellington, Marlborough and Canterbury are expecting north-west gusts of up to 160 km/h.
Metservice warns that winds of this strength could bring down trees and power lines, damage unsecured structures, lift roofs and make travel hazardous.