NASA explains that the Pineapple Express is what’s known as an atmospheric river, a slow-moving low-pressure center that brings tropical moisture from the Hawaiian Islands to the West Coast. A subtropical jet steam carries the moisture over the Pacific, and it turns to rain once it hits the coastal mountains. Recently, it’s been bringing much-needed water to California.
The first storm arrived in the middle of the week of January 2, according to NASA, and it was followed by another storm over the weekend of January 7. Although the drought-plagued state appreciated the heavy rainfall, NASA notes that it did cause flooding, hurricane-force winds, and some nasty mudslides. The agency expects several feet of snow in the interior of the state.
NASA is able to track the Pineapple Express thanks to the Multi-satellite Precipitation Analysis (TMPA) at the NASA Goddard Space Flight Center in Greenbelt, Maryland. TMPA uses Tropical Rainfall Measuring Mission satellite (TRMM), the first precipitation radar in space, and its successor, the Global Precipitation Measurement mission (GPM).
Both the TRMM and GPM are joint ventures between NASA and the Japanese space agency, JAXA. Columbia Pictures, the studio behind the movie Pineapple Express, is not involved.