Heavy rain and gales are expected to batter parts of the South Island today

A front, preceded by a strong moist northwesterly flow is expected to move slowly east onto the far south of the South Island.

Orange heavy rain warnings are in place for Westland, Fiordland and the headwaters of both the Canterbury and Otago lakes until tomorrow afternoon.

MetService says Fiordland's rainfall amounts are unusually large, so streams and rivers are likely to rise rapidly and damage to trails and roads is possible.