Pineapple Express

Pineapple Express is a non-technical term for a meteorological phenomenon, a specific recurring atmospheric river characterized by a strong and persistent large-scale flow of warm moist air, and the associated heavy precipitation both in the waters immediately northeast of the Hawaiian Islands and extending northeast to any location along the Pacific coast of North America. A Pineapple Express is an example of an atmospheric river, which is a more general term for such relatively narrow corridors of enhanced water vapor transport at mid-latitudes around the world. Causes and effects A Pineapple Express is driven by a strong, southern branch of the polar jet stream and is marked by the presence of a surface frontal boundary which is typically either slow or stationary, with waves of low pressure traveling along its length. Each of these low-pressure systems brings enhanced rainfall. The conditions are often created by the Madden–Julian oscillation, an equatorial rainfall pattern which feeds its moisture into this pattern. They are also present during an El Niño episode.