Rain, hail and thunderstorms are expected in parts of Canterbury as temperatures fall.
MetService has issued a severe thunderstorm watch for the Canterbury High Country, Marlborough and Nelson from noon until 9pm on Friday.
It said the low pressure system moved east onto New Zealand this morning.
Canterbury temperatures have dropped from 21 deg C yesterday to a high of 17 deg C today and on Saturday then down to 14 deg C on Sunday.
"An unstable atmosphere, daytime heating and wind convergence are forecast to generate showers and thunderstorms over the northern South Island today," a MetService spokesperson said.
"For the far north of Canterbury, Marlborough, eastern Nelson/Tasman and the Nelson Lakes District, there is a moderate risk of severe thunderstorms bringing downpours of 25 to 40 mm/h, and large hail (>20 mm diameter) and/or significant hail accumulations.
"Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.
"Large hail can cause significant damage to crops, orchards, vines, glasshouses and vehicles, as well as make driving conditions hazardous."
The cool temperatures in the upper atmosphere will also bring unsettled weather to central and northern parts of the country.
There was a moderate risk of thunderstorms for Waitomo, Taranaki, Horowhenua, Kāpiti Coast, western Tasman and Buller, with 10-15mm of rain per hour expected.
Localised heavy falls of 10 to 20mm/h and hail of 5 to 15mm diameter were possible.
MetService said another low-pressure system was forecast to spread across New Zealand on Friday, bringing rain or showers to many areas.
"Thunderstorms with hail are possible over many central and northern parts of the country during Friday."
- APL
