MetService is advising Dunedin residents to clear their drains and gutters in preparation for heavy rain and surface flooding.
The weather forecast for the 33 hours, starting at 3am on Thursday through to noon on Friday in North Otago, Dunedin and Clutha, is for periods of heavy rain, in amounts which ‘‘may approach or even exceed’’ warning criteria.
A heavy rain watch has been issued for those areas, and MetService said the chance of it being upgraded to a warning was high.
A brief period of heavy rain was expected tomorrow afternoon and evening, before easterly rain sets in on Thursday morning.
Niwa data showed normal rainfall in Dunedin could reach 60mm in the month of October, but the rainfall totals over the next three days could exceed that.
MetService said streams and rivers may rise rapidly, and surface flooding, slips and difficult driving conditions were possible.
‘‘Clear your drains and gutters to prepare for heavy rain.
‘‘Avoid low-lying areas and drive cautiously.’’
Emergency Management Otago stakeholder engagement adviser Erica Andrews said the organisation would continue to keep a close eye on the situation, and advised residents to keep up to date with the latest forecasts and check their website for information.
Earlier, MetService meteorologist Lewis Ferris said today’s weather would become cloudier as the day progressed, northeasterly winds would pick up, and some rain would start to fall around the southwest of the country.
Then tomorrow, a front preceded by a strong moist northeasterly flow would move slowly east on to New Zealand, he said.
"Wednesday and Thursday are the main risk period for severe weather, and heavy rain watches are already in force for western and northern parts of the South Island."
A heavy snow watch for Central Otago and Queenstown Lakes was updated this afternoon for 12 hours from noon tomorrow.
Periods of heavy snow above 700m are expected, where snowfall amounts may approach warning criteria.
MetService meteorologist Mathapelo Makabulane said the snow could hit the southern mountain passes.
"We are still in snow season and we see the return of some snowfall in the Otago region, Southern Lakes into parts of Central Otago," she said.
"If people are going to be travelling on those high level roads, places like the Haast Pass, Lindis Pass, Crown Range Road, we could see some snow settling on those roads."
Road snowfall warnings have been for the Crown Range Rd, Milford Rd (SH94), Lindis Pass (SH8) and Haast Pass (SH6).
The unseasonable wintry conditions are likely to stress livestock and bring travel disruptions.
NZ Transport Agency Waka Kotahi said that given the school holidays were under way, drivers needed to take extra care as roads would be busy.
“It is essential people drive to the conditions and be prepared for hazards on the road,” said NZTA Journey Manager Tresca Forrester.
The Milford Road will close at 5pm today owing to an increased avalanche risk. With more rain and snow in the forecast it may remain closed on Wednesday, NZTA said.
Ferris said the "potentially severe weather" was brought about by a low pressure system approaching from the Tasman Sea, "which drags some warm and humid air across our shores".
"While this does mean some warmer than average temperatures, it also increases the chance of heavy rain as the system passes over.
"Strong northeasterly winds will also be seen before the rain arrives."
On Friday, a slow-moving front and a moist easterly flow were expected to bring more rain to the southeast of the South Island.
"Prolonged rain is also possible around these areas and severe weather forecasts might be issued", Mr Lewis said.
The rain was expected to ease on Saturday.
While it was still too early to say if the heavy rainfall would cause any flooding, Emergency Management Otago stakeholder engagement adviser Erica Andrews said the organisation would be keeping a close eye on the situation.
- additional reporting RNZ
