Look out! Here comes the "pineapple express"

“Pineapple express” is a nickname for a strong atmospheric river that originates in the tropical Pacific near Hawaii. Other names for this phenomenon are tropical plume, tropical connection, moisture plume, water vapor surge, cloud band and "sky tsunami”.

An atmospheric river is a long plume of moisture that stretches from the tropics or subtropics into higher latitudes, often thousands of miles long. Formed by winds associated with cyclones, atmospheric rivers typically range in size from 250 miles to 375 miles in width and move under the influence of other weather conditions. They can transport vast amounts of water vapor, equivalent to the flow of the Mississippi River.

After transporting the moisture, atmospheric rivers dump the moisture as rain or snow in cooler regions. These long, narrow bands of concentrated water vapor look like rivers when viewed from satellites.

Atmospheric river systems are crucial for replenishing water supplies in many regions. Especially significant on the west coast of the United States, atmospheric rivers create 30% to 50% of annual precipitation. They can also cause weather-related hazards including land slides and mudslides. Atmospheric river flooding has become one of the most destructive and least understood drivers of disasters in the western United States. The worst impacts occur when atmospheric rivers are intense, hit mountains, and/or arrive repeatedly, so the landscape and rivers have no chance to recover between storms.

Once virtually unheard-of outside meteorology circles, atmospheric rivers have inundated the U.S. with increasing frequency over the last several years. Monitoring atmospheric rivers is essential for weather forecasting and disaster preparedness. 

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