Tauranga residents are in for as much as 200mm of rain with a severe weather watch issued for the Bay of Plenty for today and tomorrow.
Residents are being warned of flooding, slips and hazardous driving conditions.
Metservice expected the watch to be be upgraded to a severe weather warning because there was the possibility of 200mm of rain falling.
According to the Metservice, a strong northeasterly flow was expected to bring a very warm, moist air mass on to the country.
This was likely to bring large amounts of rain and severe gales.
Meteorologist Angus Hines said there was a "little bit of uncertainty" about the amount of rain that would fall, but expected showers this morning which would turn into heavier rain tonight.
The "significant falls" were expected tomorrow.
However, he expected weather to be better for Easter holiday-makers.
"The general trend is for most of the severe weather to pass by Easter," Mr Hines said.
"The heavy rain should clear by the weekend, it's looking pretty good."
The Eastern Bay of Plenty would be the last place the high pressure systems would cross, with the heavier rain falling into Friday.
Rainfall accumulations could reach warning amounts in the Bay of Plenty, Northland, Auckland, Taranaki, Coromandel Peninsula, Rotorua, Taupo and the far north of Gisborne.
A band of heavy rain was expected to move onto Auckland and Taranaki tonight and then spread east during tomorrow.