A severe thunderstorm watch is in place for many parts of the central North Island.

MetService says unstable, humid conditions are expected to produce scattered thunderstorms, with potential downpours of up to 40 millimetres an hour.

Some of them could be severe, dumping as much as 40mm of rain per hour and even some hail.

Hail stones of up to 15 millimetres in diameter could be produced from these conditions.

Affected areas include Waikato, Waitomo, Bay of Plenty, Rotorua, Taupo, Gisborne, Hawkes Bay and Taihape from this afternoon.

A shift in the weather means relief for parched farms in parts of the South Island, and some dramatic storms in the North.