The remnant energy of ex-tropical cyclone Debbie formed an 'atmospheric river', a rare weather event linked to the deluge which soaked the country this week.
The tropical storm forced about 2000 residents out of their homes In Edgecumbe when the Rangitaiki River burst through a stopbank on Thursday and caused flooding and destruction across the country.
Niwa forecaster Ben Noll said atmospheric rivers, described as long, narrow regions in the atmosphere transporting water vapour, only occur about 40 days out of the year and are linked to about half the country's rainfall extremes.
He said this week's tropical torrent produced up to three times the normal April rainfall for some locations in just three days.
Whakatane District entered its second day in a state of emergency as floodwaters continue to swamp the eastern Bay of Plenty. About 2200 people are holed up in homes in isolated communities unable to go any where.
