Flooding in Tasman last week. Photo: RNZ/Mark Papalii
A heavy rain watch for the top of the South Island has been extended, and will be possibly upgraded to an orange warning on Thursday morning for some areas.
MetService said periods of heavy rain were expected north-west of Motueka, between 3pm Wednesday and midnight Friday.
Another burst of heavy rain in Tasman was expected on Friday, with heavy rain also expected from early Friday afternoon in other areas in Nelson and Marlborough.
Tasman District Council's hydrology team said the rain over Wednesday would be heaviest in the coastal parts of Golden Bay rather than the ranges, with low rainfall intensities.
The rain on Friday was expected to be heavier in the ranges and double the amount forecast for Wednesday, with between 140 to 180mm expected to fall.
The council said that could cause moderate flooding in the Tākaka and Aorere rivers (up to annual flood), surface flooding and exacerbate the issues of high groundwater levels in the lower lying areas and possibly put further pressure on slope stability.
In Nelson the highest rainfall is expected in the eastern ranges from Friday afternoon, with a possibility of 70 to 90 mm falling and lesser amounts around Nelson city.
The council was not expecting flooding in any of Nelson's main rivers but said the rain was likely to cause surface flooding in low-lying areas that had recently been flooded and possibly further landslips. With increased wind and sodden ground, there was also the risk of trees falling.
There was still uncertainty between the rainfall models and it would have a better idea of the rainfall intensities closer to Friday, the council said.
On Wednesday Tasman's deputy mayor said residents should hope for the best but prepare for the worst.
The region was recovering from widespread flooding that wrecked homes and farmland. Since the flooding, 15 homes have been yellow stickered and one has been red stickered. They were in the Motueka Valley, Tapawera and Wai-iti.
MetService has issued a heavy rain watch over part of the Tasman District north-west of Motueka running from 1pm Wednesday until 3am Thursday.
"It's a little bit of a concern, particularly when local soils are so wet and people are still in recovery mode. A lot of people in the community are starting to feel the weight of the previous flooding which has been quite a burden to some people," deputy mayor Stuart Bryant said.
"More rain on top of what we've already had will just exacerbate what's already happened. There'll be soft soils at places where rivers are and we're worried that it'll crumble away into the river and more productive land will be washed away and lost.
"The other risk is, of course, silt or gravel coming over your land."
He said recovery from the previous flood had been daunting.
"Every day there's appeals for people to come and help with tidying up in different areas," he said.
"Student Army and lots of groups are stepping up but of course it all takes time to organise and co-ordinate and the clean up's not going to be exceptionally quick, it'll take weeks if not months."
Rain won't be as heavy
MetService meteorologist John Law said the rain would start around 1pm and continue until the early hours tomorrow.
"It's not by any stretch the same amount of rain we've seen in the last few weeks ... but it is on top of already saturated conditions."
Northerly winds would help to push the rain into the northern and western parts of the region, around Motueka, however, the winds wouldn't be especially strong, Law said.
Another front was due to roll in on Friday and this would bring more rain for the top of the South Island and also the top of the North Island.
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