Heavy rain is expected for the eastern Bay of Plenty, also ranges of the upper South Island, and Mount Taranaki, says a MetService spokesperson.

The MetService has issued a Severe Weather Watch.

"A front over the Tasman Sea, preceded by a north to northeast flow,is expected to move east over New Zealand on Monday and become slow moving over the North Island on Tuesday," says a MetService spokesperson.

"The future progress and intensity of this front from Wednesday into Thursday is uncertain at this stage, however, a Watch is in force for a prolonged period of heavy rain about eastern Bay of Plenty which could potentially become a Warning in the coming days."

Watches are also in force for short duration heavy rain about the Tasman Mountains, Richmond and Bryant Range and Mount Taranaki.

People are advised to stay up to date with the latest forecasts in case part of this Watch is upgraded to a Warning and further areas are added.

A Heavy Rain Watch is in place for the following areas:

Area: Bay of Plenty east of Kawerau
Valid: 49 hours from 10:00 pm Monday to 11:00 pm Wednesday
Forecast: Prolonged period of northerly rain, with some heavy falls. The extent of this period is uncertain at this stage and is likely to be in bursts, however, the rain could continue into Thursday.
Rainfall totals could exceed warning amounts and a Warning is possible.

Area: Mount Taranaki
Valid: 15 hours from 5:00 am to 8:00 pm Monday
Forecast: Period of heavy rain. Rainfall amounts could reach warning criteria (greater than 75mm in 15 hours).

Area: Tasman Mountains
Valid: 10 hours from 3:00 am to 1:00 pm Monday
Forecast: Period of northerly rain. Rainfall amounts may approach short duration warning criteria (60mm in 9 hours).

Area: Richmond and the Bryant Range, including the Rai Valley
Valid: 9 hours from 4:00 am to 1:00 pm Monday
Forecast: Period of northerly rain. Rainfall amounts may approach short duration warning criteria (60mm in 9 hours).