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Parts of the South Island could get heavy rain, thunderstorms, hail and possibly damaging wind gusts today.
A cold front is forecast to move northwards across the South Island today and onto the lower North Island tomorrow where it becomes slow-moving.
This front is preceded by a moist northerly airstream and heavy rain for parts of southern and central New Zealand, and is then followed by a cooler southerly flow which could also bring heavy rain to some places, MetService advised.
Another front is expected to move over the south of the South Island this morning, then quickly up the east of the South Island from the afternoon.
Heavy rain warnings were issued last night for Westland, the West Coast and the top of the South Island. Rain would continue to affect parts of Westland and the Canterbury headwaters from 9am until 8pm today.
For Westland between Otira and Haast: Expect a further 120 to 180 mm of rain to accumulate about the ranges on top of what has already fallen, bringing rainfall totals for the event to 400 to 500 mm or possibly more. Coastal areas can expect a further 60 to 90 mm of rain to accumulate.
For the headwaters of the Canterbury lakes and rivers about and south of Arthurs Pass: Expect a further 100 to 150mm of rain about the divide, and 50 to 70mm within 15km east of the divide.
Thunderstorms on east coast
MetService forecaster Gerard Bellam said today there was a moderate risk of thunderstorms in Dunedin, up through North Otago to Oamaru and Canterbury in the afternoon and evening.
Any thunderstorms that occur could bring localised heavy rain with intensities of 10 to 25mm/h, strong wind gusts of 90-110km/h and hail 10 to 20mm in diameter.
However, in Canterbury, south of about Rakaia, there is a moderate risk of severe thunderstorms developing, bringing a risk of damaging winds gusting greater than 110km/h and the possibility of small localised tornado.
Wind gusts of this strength can cause some structural damage, including trees and power lines, and may make driving hazardous. If any tornadoes occur, they will only affect very localised areas.
A lower risk of thunderstorms extends inland from Clutha to North Canterbury.
The mercury in Christchurch yesterday hit 30degC - about 9degC higher than normal for this time of the year.
Bellam said Christchurch and Kaikōura would be in the high 20s today before the temperatures "drop off the cliff" to the low teens in Timaru and Ashburton tomorrow.
- ODT Online and NZ Herald