And how do meteorologists determine how “heavy” rainfall is? The science of measuring rainfall Put simply, a rainfall measurement is the depth of water that has fallen over a given period of time.

Within a week's time, the northern Philippines were hit by two tropical cyclones that left behind more than 42 inches of rainfall to various areas, and NASA's Tropical Rainfall Measuring Mission ...

That amount of rain has been seen only twice before since the weather service began measuring rain 80 years ago – in December 1951 and in January 1969.