The forecast is for rainfall of 30 to 60 mm on top of what has already started to fall in areas.
The agency said a complex low-pressure trough continues to bring heavy rainfall to the region, and people are urged to stay abreast of the latest forecasts.
It warned that the heavy rain could cause streams and rivers to rise rapidly, with possible flooding and slippage, making driving conditions dangerous.
The orange warning will remain in effect until 1 p.m. today.
Meanwhile, meteorologists say another complex trough is moving into the North Island tomorrow and the heavy rain watch for Gisborne and Coromandel Peninsula is now in effect from 9am tomorrow morning until 3am Tuesday morning.
Tropical low is being ‘closely monitored’
Meteorologists are closely monitoring a weather system near Fiji that has the potential to morph into a new tropical cyclone.
But MetService said it’s too early to know if that would happen and whether New Zealand will be affected.
“There is a tropical low, 8F is the technical name right now, that was analyzed this morning north of Fiji,” said meteorologist Ciaran Doolin.
“There is a low risk of it forming a tropical cyclone today.”
However, that risk would increase to “moderate” in the coming days.
There was also another low over the Coral Sea, which Doolin described as “poorly organized at the moment”, which also had a chance of becoming a tropical cyclone. It should head towards Vanuatu early next week.
But it was still too far away to make solid predictions about both weather systems and their movements.
“We’re talking about a pretty long range now for a system that isn’t even called a tropical cyclone.
“The really long-range projections right now have this system moving a little bit to the east of the country, pretty far east. . . but we need to highlight a lot of uncertainty. We will have much more certainty in the coming days.”
What worried New Zealanders more was a potentially heavy downpour that moved across the eastern parts of the North Island on Monday and Tuesday.
“That’s probably going to be more important to most people,” he said.
The flood-ravaged areas of Auckland and Hawke’s Bay, along with the Bay of Plenty, were at low risk of heavy rain, while Gisborne and the Coromandel were at moderate risk of heavy rain, he said.
There was currently a “band of moisture” off the coast, but easterly currents would push it across the eastern and northern parts of the North Island.
“That’s probably the most immediate thing to look for.”
Meanwhile, the South Island could expect good weather in the coming days, with rain in the middle of the week. The west coast is expected to take the brunt of the weather.
Around that time, the weather for the North Island is expected to ease, and in the meantime Wellington would be “neither the worst nor the best off”.
The weather for the coming week
Doolin said next week would be a bit of a “see-saw” across the country, with sunshine in the south and rain in the north on Monday and Tuesday, and vice versa.
Around Monday and Tuesday, there was a moderate risk of heavy rain in the Coromandel and Gisborne areas, and a low risk of heavy rain for Auckland, Bay of Plenty and Hawke’s Bay.
Doolin said there was an easterly current that pushed the rain over the northeastern parts of the country.
That’s probably the most direct thing to look for for the North Island,” he said.
Meanwhile, the South Island continued to see “pretty nice weather for the most part” and would remain that way for the first part of the week.
“However, they will see a front come over them by the middle of next week, which means conditions will worsen for them.”
The west coast would likely be affected, he said.
The weather in the North Island will start to improve by then.
“It’s a bit of a see-saw going on.”
Wellington will experience a little bit of everything, he said.