MetService has issued a thunderstorm watch for Whanganui for Monday afternoon.
The storms, which could be accompanied by heavy rain, are likely to affect much of the central and lower North Island, including Whanganui, Taumarunui, Taupo, Hawke's Bay, Taranaki, Taihape, Manawatu, Tararua, Kapiti-Horowhenua and Wairarapa.
In a statement, MetService said a severe thunderstorm watch means conditions are favourable for severe thunderstorms in and close to the watch areas.
"People in these areas should be on the lookout for threatening weather conditions and monitor for possible severe thunderstorm warnings," MetService said. A warning means a higher level of risk than a watch.
The statement said there was a moderate risk that one or two of these thunderstorms could be severe, producing localised downpours of 25 to 40mm per hour, especially about the ranges.