Wrapping up a very wet week

July 23, 2017

Over the last few days, a slow-moving rain band bought some very large rainfall accumulations to places in the east of the South Island that typically don’t see a large amount of rain at this time of year.

From Thursday, a low pressure system near central New Zealand funnelled a stream of humid air towards the east coast of the South Island. This system was slow moving and delivered persistent and heavy rain to the area, causing flooding, slips and road closures. Most places from Christchurch to Dunedin recorded more than the long-term average July rainfall in just 24-48 hours. “In some places this comparison was even more stark: The weather station at Oamaru airport reported 147mm throughout the event, which more than triples the July average rainfall of 40mm.” said MetService meteorologist Angus Hines. Due to the severe weather and flooding, a state of emergency was called in many South Island towns and cities, including Christchurch.

As the clean-up from this event gets underway, Sunday is a clear, dry day for much of the South Island. However, cold temperatures and excess rain water have created conditions favourable to the formation of black ice in sheltered and shady spots. This is likely to be the case again in the coming night, so drivers are advised to be alert on the roads. Elsewhere, showers and cloud are affecting the fringes of the North Island, and the top of the country from Auckland northwards, but a decent day is in store for most places in between.

A pair of fronts are in line to move northwards over the South Island over the coming few days, this time bringing the heaviest rain to western areas. A heavy rain warning is in place for a burst of heavy rain in Fiordland early on Monday morning, while a Severe Weather Watch for heavy rain has been issued further up the west coast. Drenched places in the South Island will briefly see scattered rain on Monday, although nothing like the intensity of the rain they have had in the last few days. Another brief dry spell looks likely after this, but all eyes will be on the forecasts for Thursday, when another cold southerly rain event looks likely to affect Canterbury and much of the South Island.

Radar accumulation over the final 24 hours of the rain event in the South Island. Shows accumulations of over 100mm across Banks Peninsula and east of Christchurch.

Official Severe Weather Watches and Warnings are reviewed and re-issued by MetService at least every twelve hours, and more often if necessary. To get the most up to date information on severe weather around the country, or any other forecasts, see metservice.com or on mobile devices at m.metservice.com. You can also follow our updates on MetService TV, at MetService New Zealand on Facebook@metservice  and @MetServiceWARN on Twitter and at blog.metservice.com 

 

MetService issues Warnings, Watches and Outlooks for severe weather over New Zealand.

Warnings are about taking action when severe weather is imminent or is occurring. They are issued only when required.
Recommendation: ACT 

Watches are about being alert when severe weather is possible, but not sufficiently imminent or certain for a Warning to be issued. They are issued only when required.
Recommendation: BE READY 

Outlooks are about looking ahead, providing advance information on possible future Watches and/or Warnings. They are issued routinely once or twice a day.
Recommendation: PLAN 

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