Heavy rain watches have also been issued over the Gisborne ranges, north of Tolaga Bay and Tasman, northwest of Motueka in the South Island, where rainfall amounts may approach warning level.
People are advised to keep up to date with the latest forecasts in case any watches are upgraded to warnings, or further areas are added.
Thunderstorms are expected to develop over the southern half of the South Island this afternoon and evening, bringing heavy rain with intensities of 15 to 25 mm/h and hail 10 to 20 mm in diameter.
There is a risk that some of these thunderstorms could become slow-moving and severe, producing localised downpours of 25 to 40mm.
Rainfall of this intensity can cause surface and/or flash flooding, especially in 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.
Looking ahead to the weekend, there is a chance of heavy rainfall throughout most of the country from Saturday December 17 to Tuesday December 20.
There is forecast to be high humidity over the whole North Island and much of the South Island this weekend.
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
MetService advises that 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
