Forecasters say 'Pineapple Express' storm will probably be beneficial for Los Angeles and Ventura counties, helping to reduce the risk of wildfires.

A Pineapple Express forms when the jet stream dips south into the tropical Pacific near Hawaii, scooping up warm, moist air and carrying it northeast across the ocean. Named for Hawaii's famous fruit and the storm's origins near the islands, these powerful systems can dump the equivalent of 10 to 15 inches of rain over two to three days.

For the second time this year, Southern Californians are evacuating their homes as heavy rain threatens new destruction in areas still recovering from last month’s devastating wildfires.