"Exceptionally" heavy rain, bound for the west of the South Island this week, has prompted MetService to consider issuing a rare 'Red' weather warning.
MetService meteorologist David Miller said a ridge of high pressure that brought mostly settled weather over the weekend, was now set to move to the east of the country early this week, allowing a warm northerly flow to spread.
However, a frontal system within this northerly flow was expected to become slow-moving over the west of the South Island and MetService Orange heavy rain warnings have been issued, he said.
"This front will bring significant accumulations of rain to northern and western parts of the South Island, with rain developing there overnight Monday into Tuesday.
"During this time, up to 500mm and perhaps even higher amounts in places, may be recorded, with the largest amounts expected in the ranges.
"Significant impacts can be expected, such as slips, flooding and rapidly rising rivers and streams.
"This event is exceptional, not just in its accumulation amounts but also its prolonged nature, with heavy rain expected to continue in these areas right up until Thursday evening."
He said MetService severe weather meteorologists would be in close contact with regional council hydrologists and Civil Defence during this event and would collaborate to decide whether the Orange rain warning should be upgraded to a Red warning.
"Red warnings are reserved for only the most extreme weather events and requires immediate action to protect people, animals, and property from the impact of the weather."
On a more positive note, he said the frosty temperatures observed last week would be a distant memory, and temperatures were expected to be warmer than average this week.
"Looking ahead to this weekend, models are indicating that another front may bring yet more heavy rain to western parts of the South Island.
"This will be closely monitored by MetService meteorologists throughout the week."
