A severe weather warning has been issued for Nelson and central and southern parts of the North Island.

Humid conditions are forecast for Saturday and the MetService says this makes it favourable for severe thunderstorms in Nelson, Taupo, Taihape, Whanganui, Hawke's Bay, Manawatu and the Tararua district.

Torrential rain of up to 40mm per hour and hail is possible.

"Rainfall of this intensity can cause flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips," MetService says.

"Driving conditions will also be hazardous with surface flooding and poor visibility in torrential rain."