MetService is forecasting thunderstorms, heavy rain and hail for coastal Otago, Southland and Fiordland tomorrow.
During Wednesday afternoon and evening, upper temperatures will continue to cool over southern New Zealand, while a surface front continues to move northwards over the South Island.
A MetService spokesman said as a result, there was a "moderate risk'' of thunderstorms during the afternoon for Fiordland, Southland, Clutha and Dunedin.
"Any thunderstorms that occur will likely be accompanied by heavy rain of 10 to 25mm per hour, plus small hail from South Westland to Dunedin.''
In addition, during the afternoon and evening, there was a "moderate risk'' of thunderstorms for North Otago and the Canterbury Plains and foothills from about Methven southwards, he said.
If thunderstorms eventuated in this area, they too would likely be accompanied by heavy rain of 10 to 25mm per hour and small hail.
Despite autumn's official arrival on Friday, the MetService forecast shows temperatures around the region will return to the mid-20s next week.
