Met Service have issued a severe weather warning for the Nelson region with periods of heavy rain expected until Wednesday afternoon.
A further 120-140mm of rain is expected to accumulate about the ranges, with 70 to 90mm possible elsewhere.
Peak intensities of 15-25mm per hour are expected tonight and Wednesday morning with thunderstorms.
Showers are forecast to continue into Wednesday evening.
110-130mm is expected in the Richmond Ranges with possible thunderstorms as well.
Freezing level is 2000 metres.