Downpours forecast to hit eastern Otago today are set to drench the region for more than 24 hours.
MetService meteorologist Lisa Murray warned heavy rain was expected on the east coast of Otago from about 3am today.
The heavy rainfall from Dunedin to North Otago was forecast to continue until 6am tomorrow.
Up to 120mm of rain could fall as the slow-moving southeast front hit after crossing the Tasman Sea, Ms Murray said.
Residents should clear gutters and drains because up to 15mm of rain could fall in an hour. Clogged drains could cause surface flooding, she said.
The spell of heavy rain would be bookended by periods of ''patchy rain''. The rain was forecast to ease later tomorrow with patchy drizzle on Good Friday.
Raineffects director Dave Stewart said Dunedin soil moisture levels were ''down a bit'', as it had been a week since the last significant rainfall.
The soil would be able to absorb some of the rain, but some ''run-off'' should be expected.
If 120mm of rain fell, surface ponding of water and possibly slips - especially on Otago Peninsula - should be expected.
South Dunedin should avoid flooding if the mud-tanks and pumps had been maintained correctly, Mr Stewart said.
The Dunedin City Council said the heavy rain, combined with a high tide at 4.30pm today and again tomorrow morning, may cause surface ponding and manhole covers could lift.
Council infrastructure and networks general manager Ruth Stokes said council staff and contractors had been preparing for the rain and the city's stormwater screens were clear.
Contractors had also been sweeping gutters around the city, and the council called on residents to clear leaves from grates outside their home to help water flow into drains.
Mrs Stokes said residents who noticed flooded mud-tanks should call the council so contractors could be organised.
Otago Regional Council engineering, hazards and science director Gavin Palmer said Otago experienced rainstorms like the one forecast about once a year.
Most rivers and streams in eastern Otago, particularly the Shag, Water of Leith and Lindsay Creek, Silver Stream, Tokomairiro, and Pomahaka rivers, were expected to rise from tomorrow. Later, the Taieri River at Outram was likely to be high.
Mr Palmer said based on forecasting, rivers and flood channels should be able to contain the rainfall safely .
South Dunedin groundwater levels were not high, but were ''likely to rise''.
Niwa climate scientist Gregor Macara said the highest daily rainfall recorded in Dunedin in April was 229mm in 1923.
In the Bay of Plenty, 57 schools and about 80 early learning services have been advised by the Ministry of Education to close today as a precaution ahead of further heavy rain.
Social Development Minister Anne Tolley and Primary Industries Minister Nathan Guy yesterday classified Bay of Plenty damage from Cyclone Debbie as a ''medium-scale adverse event''.
Additional recovery assistance available included recovery co-ordination and increased support through Enhanced Task Force Green teams and the Bay of Plenty Rural Support Trust.
