The Bay and Coromandel region has already had a month's worth of rain this week - and another month's worth is about to fall.
MetService meteorologist Peter Little said a warning was in place for heavy rain in both the Coromandel and Bay of Plenty. It was expected to hit from midday today in Coromandel and about 3pm in the Bay.
The rain would carry right through until tomorrow morning.
Mr Little said both regions could expect around 120mm to 140mm of rain in that time.
"You're in for another month's worth of rain again in that period," he said. "The ground is going to be getting a lot more rain yet before it can dry out."
Mr Little said the rivers in the Bay and Coromandel were already "fairly swollen" in places and more rain was only going to exacerbate the problem.
But there was some good news, Mr Little said - it wouldn't be cold.
"Overnight temperatures will be about 20C. There will be no need to wear socks to bed.
"It will be very warm and very muggy."
There was also a risk of thunderstorms, and people needed to be aware the rain may not be continuous but wax and wane, so should be careful of making any outdoor plans.
The weather would not be clearing until the start of the next working week, Mr Little said.
Road crews remain in a state of readiness across the Bay, with the next deluge increasing the likelihood of more slips, downed powerlines and flooding.
Transport Agency regional performance manager Karen Boyt said the slips near Whangamata and Whiritoa were being cleared as quickly as possible.
"The crews are still out clearing debris around the district so we'd like people to watch their speed and continue to drive carefully."
State Highway 25 at Whangamata was expected to remain closed this morning, due to several large slips. Contractors have also come across power lines on the road, so it was not expected to open until 5pm today.
Residents living on that section of highway have been given special access.
Closer to Waihi, SH25 was expected to be open by this morning.
The first round of heavy rain caused no major issues in the Tauranga City Council area, said a spokesman.
The city's stormwater systems had so far coped with the deluges.
Contractors are checking for potential stormwater blockages around the city.
The council is encouraging people to clear debris from gutters in their streets if possible, to help prevent flooding.
Friday: Rain, turning heavy. High of 23C, low of 20C. Northeasterly.
Saturday: Rain, heavy falls, chance thunderstorm. High of 25C, low of 20C. Northerlies.
Sunday: Rain, chance heavy. High of 25C, low of 19C. Winds turn northwest.
Monday: A few showers. High of 25C, low of 16C. Westerlies.