A rain watch issued for the Coromandel region on Tuesday morning, remains in force today.

The MetService is forecasting heavy rain for parts of the North Island and upper South Island.

"A slow-moving low just west of the North Island is expected to pass a front east over the North Island today," says a statement from the weather organisation.

"This front brings periods of northerly rain to much of the North Island and upper South Island.

"Meanwhile, another weaker front is moving northwards over the South Island bringing a southerly change.

"The heaviest rain is expected about parts of the North Island and upper South Island, with thunderstorms and localised downpours also forecast."

HEAVY RAIN WATCH

Area: Auckland and Coromandel Peninsula

Valid: 5 hours from 9am to 2pm Wednesday

Forecast: Periods of heavy rain, with thunderstorms and localised downpours possible. Rainfall accumulations may approach warning criteria in some places.

Area: The Marlborough Sounds

Valid: 15 hours from 6am to 9pm Wednesday

Forecast: Periods of heavy rain, with thunderstorms possible.Rainfall accumulations may approach warning criteria.

Area: Wellington

Valid: 10 hours from 8pm Wednesday to 6am Thursday

Forecast: A period of heavy rain. Rainfall accumulations may approach warning criteria.