Metservice said isolated thunderstorms were expected from about 2pm until 8pm today for inland North Otago, inland Dunedin, eastern Central Otago, Clutha, Southland and South Fiordland.
A heavy rain watch has also been issued for Fiordland.The heat alerts have been issued for Dunedin, Invercargill and Oamaru with temperatures expected to exceed 30degC on both tomorrow and Friday this week.
The heat alert system is being trialled by MetService this summer to give extra warning to vulnerable people when temperatures are likely to be significantly above normal.The sweltering conditions are not expected to last long though with temperatures likely to drop by as much as 15degC in Gore by Wednesday next week.
The forecast thunderstorms are expected to be slow moving, increasing the risk of heavy localised downpours of 25-40mm per hour.
They warned rainfall of this intensity could cause flash flood especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.
Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain.
A MetService spokesman said the "unsettled" weather caused by the same weather pattern that was causing flooding and mayhem in the North Island.
The National Emergency Management Agency advises that as storms approach you should:
- Take shelter, preferably indoors away from windows;
- Avoid sheltering under trees, if outside;
- Get back to land, if outdoors on the water;
- Move cars under cover or away from trees;
- Secure any loose objects around your property;
- Check that drains and gutters are clear;
- Be ready to slow down or stop, if driving.
During and after the storm, you should also:
- Beware of fallen trees and power lines;
- Avoid streams and drains as you may be swept away in flash flooding.
- Additional reporting RNZ
