MetService has issued a severe weather watch for Coromandel Peninsula and western Bay of Plenty.

"Heavy rain may affect Coromandel Peninsula and western Bay of Plenty overnight," says a MetService spokesperson.

"A low is expected to lie slow moving just east of the Coromandel Peninsula this evening and overnight but then move away to the east.

"Slow moving bands of rain associated with this low may affect the Coromandel Peninsula and the west of the Bay of Plenty.

"Localised downpours of 20-30mm per hour are possible, which could occur with or without thunderstorms."

The heavy rain watch for Coromandel Peninsul and Bay of Plenty west of Te Puke is in place for 12 hours from 8pm, Wednesday, July 31 to 8am, Thursday, August 1. 

Periods of heavy rain, and amounts may approach warning criteria.

People are advised to keep up to date with the latest forecasts.