MetService said streams and rivers may rise rapidly with surface flooding, slips, and difficult driving conditions possible.
“Clear your drains and gutters to prepare for heavy rain. Avoid low-lying areas and drive cautiously.”
A strong wind watch is also in place for Rotorua, Bay of Plenty east of Maketū, Gisborne, and Taupō from midnight tonight until 10am Thursday.
Northeast winds may approach severe gale in exposed places.
MetService meteorologist Lewis Ferris said the wet weather was caused by a low-pressure system approaching the country from the north.
“It’s got quite warm, humid air, which is very good potential for heavy rain and also does bring that risk of maybe some downpours or some thunderstorms.
“So, within the band of rain, there’ll be patches of what could be quite intense rain.”
He stressed that this is mainly an issue in the north of the country on Wednesday, with much of the rain moving south on Thursday.
Rain will clear to fine weather on Thursday morning in the Bay of Plenty with clear skies Friday and Saturday, and a chance of a morning shower.