Periods of heavy thundery rain are being forecast for upper parts of the North Island and west of the South Island.

The MetService says severe north to northwest gales are possible.

A severe weather warning and watch is in force for the Bay of Plenty.

'An unstable northwest flow with embedded fronts spreads over New Zealand during Tuesday and Wednesday,” says a spokesperson for the weather organisation.

'This system is expected to bring periods of heavy rain and possible thunderstorms to much of the country, especially to the north and west, along with north to northwest gales.

'The heaviest falls are expected in northern and central parts of the North Island along with Westland and northern Fiordland.

'A heavy rain warning and watches are now in force for these areas.

'Strong wind watches are also in place for parts of the upper North Island and the Canterbury High Country.”

Heavy Rain Warning - Orange
Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.
Area: Bay of Plenty east of Opotiki, also the ranges of Gisborne and north of Ruatoria
Valid: 16 hours from 2pm Tue 22 Nov to 6am Wed 23 Nov
Forecast: Expect 90 to 140mm of rain with thunderstorms. Peak rates of 15 to 25mm/h, but up to 35mm/h in possible downpours.
Heavy Rain Watch
Area: Northland, especially in the north and east
Valid: 18 hours from 6am Tue 22 Nov to 12am Wed 23 Nov
Forecast: Periods of heavy rain with thunderstorms and downpours possible. Rainfall amounts may approach warning criteria.
Area: The central North Island high country, also North Taranaki including the mountain
Valid: 17 hours from 2pm Tue 22 Nov to 7am Wed 23 Nov
Forecast: Periods of heavy rain with thunderstorms and downpours possible. Rainfall amounts may approach warning criteria.
Area: The ranges of Westland south of Otira and Fiordland north of Doubtful Sound
Valid: 12 hours from 5am Tue 22 Nov to 5pm Tue 22 Nov
Forecast: Periods of heavy rain with thunderstorms possible. Rainfall amounts may approach warning criteria.
Strong Wind Watch
Area: Northland
Valid: 5 hours from 7pm Tue 22 Nov to 12am Wed 23 Nov
Forecast: Northerly winds may approach severe gale at times.
Area: Auckland and Coromandel Peninsula
Valid: 7 hours from 8pm Tue 22 Nov to 3am Wed 23 Nov
Forecast: Northerly winds changing westerly around midnight. Winds may approach severe gale at times
Area: Bay of Plenty and Gisborne
Valid: 10 hours from 8pm Tue 22 Nov to 6am Wed 23 Nov
Forecast: North to northwest winds may approach severe gale at times.
Area: Canterbury High Country
Valid: 6 hours from 8am Tue 22 Nov to 2pm Tue 22 Nov
Forecast: Northwest winds may approach severe gale at times.