The North Island could experience more "unstable" showers and thunderstorms on Tuesday after Waikato, Auckland and Northland were battered by record rainfall on Monday.
NIWA's climate station in Māngere, Auckland, experienced its wettest hour on record between 9-10am on Monday, with 52mm of rain beating the previous record of 36.4mm.
Auckland experienced 4000 lightning strikes in just one hour on Monday - with 700 in just five minutes.
MetService warns the bad weather isn't over, with western parts of the North Island in the firing line on Tuesday.
"A broad low over the Tasman Sea will continue to direct an unstable north to northeast airstream over New Zealand during the second half of Tuesday, bringing rain or showers to many areas," MetService said.
"There is a low risk of thunderstorms for most of the North Island, as well as for the northwest of the South Island and some of its inland parts, as indicated on the chart.
"However, about western parts of Northland, the coastal northwest of Auckland, and also Gisborne north of the City, there is a moderate risk of thunderstorms; then in the evening and at night the thunderstorms risk also increases to moderate about Taranaki, the northwest of the Tasman District, and the Bay of Plenty east of Rotorua."
The forecasting company said if the thunderstorms occur they will likely bring heavy rain with intensities of 15 to 25 mm/h but Gisborne could see rain rates even higher.
The MetService currently has a heavy rain warning in place for Gisborne - until midnight on Wednesday - and the Bay Of Plenty east of Tauranga - until 9am on Thursday.
"An extended period of heavy rain is possible and this Watch will likely be upgraded to a Warning in the coming days," MetService said about the watch in place for Gisborne.
"There is a large amount of uncertainty regarding the expected rainfall during this time. From this (Monday) evening through to Tuesday night, the area most likely to receive warning amounts of rain is north of about Tolaga Bay as the flow remains north to northeasterly.
"However, from Wednesday through to early Thursday, rainfall amounts are more likely to exceed Warning criteria throughout much of the Gisborne region as the flow turns south to southeasterly."
