The quake-rattled Wellington region has received more rain in 24 hours than it would in a month.
Heavy downpours brought slips and flooding to the capital today, only hours after yesterday's magnitude 7.5 quake.
Niwa said Wellington usually received 74.8mm of rainfall at the airport for the entire month of November.
But parts of the region have received much more than that in the day following the quake.
MetService forecaster Claire Flynn said the heaviest downpours were in Wainuiomata, which recorded 109.5mm of rain in the last 24 hours.
Lower Hutt received 94.2mm, Porirua an average of about 80mm, and Wellington 59.6mm at Kelburn.
"It's definitely pretty substantial rainfall. Certainly you get events like this every now and then, but they're not common."
Flynn said the worst of the wet weather had eased, but there were still a few showers about.
Tomorrow would bring more showers, then further rain in the evening. Thursday was a similar story.
"There's a few showers around at first, but then we're getting a southerly change and it's going to be bringing some rain into the afternoon."
Niwa climate scientist Nava Fedaeff said the rain had hampered clean-up efforts this morning, with earthquake-affected areas seeing the most amount of rain around the country.
In the Upper Hutt suburb of Belmont, a whopping 83mm of rain fell between midnight and 11am today - and 15.2mm of that was in only one hour from 7am.
Parts of the quake-rattled Marlborough region had also received more than 70mm since midnight.
Fedaeff said another bout of locally heavy rainfall was expected later tomorrow through to Thursday.
"The wet weather will be accompanied by a surge of unseasonably chilly air and gusty winds from the south. Some snow may even fall across the higher terrain of the South Island.
"The relentless rains will give way to somewhat calmer weather from Friday into the weekend.
"Starting the final full week of November, warmer and generally drier conditions are anticipated. However, another period of active weather is possible toward the last several days of the month."
The wet weather comes midway through an already wet final month of spring.
Rainfall totals in some parts of the country have already topped average totals for November as a whole.
"Central New Zealand has been particularly wet, with Paraparaumu, Wellington, Hokitika and Kaikoura already receiving more rain than they would usually during the entire month," Fedaeff said.
As of Monday, Martinborough has already had its fourth wettest November since records began in 1924.
"With rain continuing on Tuesday and another half of the month still to get through, this record is only going to go up," Fedaeff said.
Palmerston North had its wettest November day on record on November 7, with 50mm recorded in 24 hours. Records extend back to 1928 there.
Meanwhile, Southland has been much drier than normal for the first half of November.
To date, Invercargill has recorded only 14mm of rain whereas the November average is 90mm.