For the first time in months, several days of heavy rain will drench B.C.'s south coast.

A powerful storm is forecast to dump as much as 120 millimetres of rain over Metro Vancouver, the Fraser Valley, Howe Sound, Whistler, the Sunshine Coast and most of Vancouver Island.

Two jet streams, one from the north, the other from the south, are pumping moisture into one nasty, late summer storm which arrived just after midnight, Friday, and should move through the region by Monday.

The heaviest downpours are expected Saturday and Environment Canada warns drought-hardened soil may not be able to absorb all the moisture, raising the risk of flash floods.

As much as 30 millimetres of rain is also forecast for mountainous regions of the Interior over the weekend, but badly-needed precipitation is not expected in wildfire-plagued areas of southeastern B.C., or in the parched central Interior.

Instead, strong winds are forecast there, increasing the risk of wildfires, but clearing the choking smoke that has hovered over much of the southern part of the province as massive forest fires burn in Washington state.