Downpours will be unleashed across many parts tonight

MetService has issued, heavy rain warnings for the Westland, Tasman, Richmond and Bryant ranges and Mount Taranaki.

Heavy rain watches also apply in Taranaki, Northland, parts of the central North Island - and the South Island.

Meteorologist John Law says the system's pushing across from the Tasman Sea.

He says western parts of the country will bear the brunt of the rain, and the Westland ranges will possibly get 160 millimetres.