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.

Evacuation orders and warnings have gone into effect for burn scar areas across Southern California as heavy rainfall threatens dangerous debris flows.