The Pineapple Express is a narrow region of atmospheric humidity that accumulates in the tropical Pacific.
Atmospheric rivers are narrow regions in the atmosphere that carry much of the moisture from the tropics to northern latitudes. Atmospheric rivers are part of the Earth’s ocean water cycle and are closely related to water supply and flood risks.
A well-known example of a strong atmospheric river is called “Pineapple Express” because moisture accumulates in the tropical Pacific around Hawaii and can hit the western shores of the USA and Canada with heavy rain and snow.
The prevailing winds cross warm bands of tropical water vapor to form this “river,” which travels across the Pacific as part of the global conveyor belt. When it reaches the west coast, the Pineapple Express can pour up to five inches of rain in California in one day.
Atmospheric rivers come in all shapes and sizes, but those that contain the most water vapor and the strongest winds are responsible for extreme precipitation and subsequent flooding. These events can affect the entire west coast of North America, often interrupting travel and damaging properties in the process.
Of course, not all atmospheric rivers are harmful. Many are weak and provide beneficial rain or high altitude snow that provide essential supplies for the water supply of Western communities.