The Tasman District Council is expecting rivers across the region to be running at high levels and is warning residents to prepare for flooding.
Heavy rain, thunderstorms, gales and possible flooding is forecast for much of the South Island.
The Tasman District council said uncertainty about the forecast and possible thunderstorms meant people should plan for flooding.
Council hydrologists said 75 to 140mm of rain had already fallen in the Tasman ranges in the last 12 hours.
The Tākaka River and its tributaries and the Aorere River had peaked or were about to peak, all below annual flood flows.
High tide coincided with the Aorere River's peak flow, so people could expect road and surface flooding in Ferntown.
Another 200 to 300mm of rain was expected in Golden Bay over the next 26 hours, along with possible thunderstorms and localised flooding.
Rivers in the region's east including the Wakapuaka, Maitai, Wairoa/Waimea and upper Motueka were also expected to reach annual flood flows.
Between 15 to 45mm of rain had already been recorded across the eastern ranges, with a further 150 to 250mm expected.
The council said there was a good chance the wet weather could cause slips, particularly on State Highway 60 over the Tākaka Hill and State Highway 6 between Nelson and Marlborough.
