Rain-laden clouds from the north Tasman sea settled over the top of the south island several days ago, and have been drenching the Nelson and Golden Bay regions ever since. Extreme rainfall has been recorded in Takaka, Richmond and Nelson, with the Kotinga gauge at Takaka recordind an unprecedented 423mm in 24 hours. The estimated 24 hour rainfall for a 1-in-100 year event at Takaka is 380mm (Tasman district council here). The previous highest recorded 24-hour rainfall from the Kotinga gauge was 216.5mm in 1995.
Saturated hillsides have given way in many locations, with landslides and debris torrents reportedly causing widespread damage in the region (stuff.co.nz story here).
Fortunately, all the news is not bad, as the rain has been easing, with heavy precipitation moving towards the North Island, where Taranaki, Northland and the Bay of Plenty can expect up to 150mm of rain.