Some North Island areas already drenched from today's deluge can expect the weather to get worse overnight.
Metservice issued a number of weather warnings for parts of the country today.
Metservice meteorologist Peter Little said the wet, unsettled weather is expected to get worse in a number of places tonight.
The forecaster has issued weather warnings for much of the North Island, include the central area around Taupō, Taumarunui and Taihape, and west across to Taranaki and down to inland Wanganui.
Warnings are also in place for Horowhenua and the Kāpiti Coast down to Wellington as well as the Marlborough Sounds.
"It is expected unfortunately get worse before it gets better," Little said.
There is a slow-moving low sitting out to the west of the country and a stubborn high which brought fine weather to the country a few days ago, he said.
"In between these two systems, we've got a very humid northerly flow and it's also very unstable, so there's a lot of thunderstorm activity."
Meanwhile, a person in Ngāruawāhia made the most of the wet weather by kayaking through the floodwater on Ellery St this afternoon.
A Ngāruawāhia resident said the flooding had since gone down and the Waikato River had swelled dramatically since the downpour, which lasted "a few good hours".
Little said the heaviest rain had been north of Hamilton and down to Cambridge, Putaruru and south of Tokoroa.
The radar at Hamilton Airport had recorded a "significant" 79.8mm of rain today.
"[That] is quite a lot given it's been very dry across much of the Waikato during the summer.
"Most of that flooding should have a chance to drain away because at the moment there is not much precipitation over that area at the moment, but there is the potential overnight to increase and come back.
"People still need to be aware that it's not over yet. There is another burst of rain, it looks like it occurs tomorrow morning ... for right across the Waikato and upper North Island."