"You will get some heavy rain. We're looking at poor visibility when driving and possible surface flooding, maybe small landslides."
People in coastal areas were at risk of isolated downpours as a result of thunderstorms.
"You've got all the ingredients for thunderstorms, you just need a decent spark to ignite it," she said.
"The thing about thunderstorms is we don't know exactly where they will bubble up."
Heavier rain is expected for the eastern ranges, with accumulations up to 250mm and downpour intensities of 40mm in an hour, Ms Murray said.
That could be followed by very strong south to southeasterly winds in exposed areas this afternoon and tomorrow morning.
She recommended people keep an eye on the forecasts and rain radars as the situation developed.
The rain was coming from the northwest of the South Island in a broad, slow-moving front expected to move east across the North Island over Thursday night and during Friday.
The path of a low containing the remnants of Cyclone Donna was uncertain yesterday, but it may pass near the east of the North Island during Friday or early Saturday as it tracks south, bringing more heavy rain and strong winds.
Mr Naude said people needed to take responsibility for their preparedness and make a plan.
"Think about what you and your family would you do if you couldn't get home, were stuck at home or had to leave home in a hurry? Would you be ready?
"What if there was no power, no water or no communication? If there is heavy rain coming, have you cleared your gutters or thought about your pets? A little bit of planning goes a long way," he said.
