It says even though red warnings have been downgraded, the ground is saturated and could lead to more slips.
MetService warns that streams and rivers may rise rapidly and could cause surface flooding, slips, and difficult driving conditions.
Wellington was hit by widespread, damaging floods and landslides overnight on Sunday and into Monday following a weekend of storms.
Authorities are urging lower North Island residents to stay off the roads and evacuate if they feel unsafe as the rain continues.
MetService said with continued rain over several days there was a possible threat to life from dangerous river conditions, significant flooding and slips.
Rain intensity 'highly unusual'
MetService says the intensity of the deluge in Wellington on Monday was highly unusual.
Forecasters pointed to the speed of the downpour, rather than the overall totals.
Meteorologist Devlin Linden said the event was highly unusual.
''The thing that makes it so impressive… is how quick the rainfall occurred," he said.
One monitoring station recorded an extreme burst, with 77 millimetres of rain falling in just one hour.
Linden said that far exceeded what is normally considered a heavy downpour.
"We consider a downpour to be anywhere between 15 to 25 millimetres," he said.
"Obviously 77 millimetres is significantly more than what we might see in a typical downpour."
Other parts of the region also experienced intense rainfall at times, with rates reaching between 25 and 35 millimetres an hour.
Linden said while it may not rank as the wettest day on record, the short bursts of intense rain had a significant impact.
"Certainly the most I have ever seen in an hour in Wellington. It was certainly a significant event," he said.
MetService said the downpours were likely linked to a thunderstorm-type system, which can produce brief but very heavy rainfall.
No update on missing man Phillip Sutton
Police say there are no updates on the man missing from Karori overnight.
They say it's unlikely there will be a plan before daylight when they are able to check conditions.
Phillip Sutton was announced as missing yesterday after floods ravaged the city.
A family member called emergency services around 7am on Monday after being unable to make contact with the man in his 60's.
Sutton's Karori South Road property was found to be hit by floodwaters and debris.
Search and Rescue teams spent hours at the site on Monday, clearing the property but have been unable to find him.
SH2 bridge washout
A bridge washout has closed State Highway 2 on the Wairarapa side of the Remutaka Hill.
The Transport Agency says Bridge 2 on the Featherston side has suffered flood damage.
Crews are on the way to assess it.
The highway will remain closed until further notice.
The Transport Agency says it is a critical route, and every effort will be made to reopen it as soon as it is safe to do so.
People should delay travel if possible.
Those who must travel between Wellington and Wairarapa should detour via State Highway 3 Te Ahu a Turanga.
This is a significantly longer route and requires extra travel time.
The only other highway closure in the area is State Highway 53 at Waihenga Bridge.
Several flights cancelled
Several Air New Zealand flights into Wellington have been cancelled this morning.
That includes flights from Gisborne, Tauranga and Christchurch and follows a number cancellations amid yesterday's severe weather.
A Wellington Airport spokesperson said in a media release to RNZ flights were landing and departing today, but there were strong winds and could be knock-on effects from previous cancellations.
The airport was advising passengers to check directly with airlines for specific flight information.
