Another round of heavy and thundery falls is on the way for the western South Island.  A pair of frontal boundaries trekking toward New Zealand will be the triggers for showers and maybe a few thunderstorms beginning tonight and lasting into tomorrow.

By early tomorrow morning, bands of heavy rain should be moving into the deep south and Fiordland.  From there, the heavy rain should move up the western part of the South Island affecting the west coast and the higher elevations.

By evening, the heavy rain will start to diminish.  However, widespread moderate precipitation will likely cover the upper parts of the western South Island.

Government forecaster MetService has issued Heavy Rain Warnings for many parts of the South Island.

Here’s the latest: 

• Fiordland north of Milford Sound – Rain is expected to become heavy in the early hours of Sunday morning. In the 10 hours from 2am to noon Sunday, expect 70-90mm rain with peak rates of 30mm/hr for several hours in thunderstorms from about 6am.

• Westland south of Otira – Rain is expected to become heavy early Sunday morning. In the 12 hours from 3am to 3pm expect 80 to 100mm rain with 130 to 150mm about the highest parts of the Southern Alps and 50-60mm near the coast. Peak rates of 30-40mm/hr can be expected in thunderstorms for several hours as the front passes.

• The ranges of Westland north of Otira and Buller – Rain is expected to set in Sunday morning and become heavy. In the 6-9 hours from 10am Sunday, expect 80-100mm northnorthwesterly rain with peak rates of 20-30mm/hr in thunderstorms for several hours from 2pm. Note, there may be a brief burst of heavy thundery rain over Buller this Saturday evening.

• Headwaters of the Lakes and Rivers of Otago – Rain is expected to become heavy on the divide early Sunday morning. In the 6 hours from 3am to 9am Sunday, expect 70mm about the divide, over 50mm with 15kms and over 30mm within 25kms of the divide. Peak rates for an hour or two of 20-30mm/hr in thunderstorms.

• Headwaters of the Lakes and Rivers of South Canterbury – Rain is expected to become heavy on the divide before dawn Sunday morning. In the 6-9 hours from 6am Sunday, expect 130-150mm on the divide, over 100mm within 15kms and over 80mm within 25kms of the divide. Peak rates in thunderstorms of 30-40mm/hr for a couple of hours, mainly near the divide as the front passes.

• Headwaters of the Lakes and Rivers of North Canterbury – Rain is expected to become heavy about the divide Sunday morning. In the 6-9 hours from 9am Sunday, expect 90-110mm about the divide, over 80mm with 15kms and over 35mm within 25kms of the divide. Peak rates near the divide of 20-30mm/hr for a couple of hours in thunderstorms.

For eastern Canterbury, including Christchurch, some rain is expected tomorrow during the late afternoon and evening.  Unfortunately, amounts are not expected to be very significant and any showers won’t last very long.  The effect on the fire danger is likely to be minimal.

Homepage image/ Christine Johnson

By Howard Joseph, WeatherWatch.co.nz and MetService