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TB4 measures highest daily rainfall record in the U.S.

August 14, 2020

49.69” (1262 mm) of rain in 24 hours recorded by TB4 tipping bucket rain gauge.

On 15 April 2018 a singular weather event occurred on the island of Kauai, Hawai’i. In a 24-hour period, 49.69 inches (1262 mm) of rain fell breaking the record for total precipitation ever recorded in the United States.

The TB4 tipping bucket rain gauge reliably and precisely recorded the historic event.

Record broken

After considering the observation and various surrounding factors, the National Climate Extremes Committee (NCEC) determined the observation to be valid. It now stands as the 24-hour record precipitation for the U.S. This data value supersedes the previous record of 43.00 inches (1092 mm) of rainfall occurring 25-26 July 1979 at Alvin, Texas during Tropical Storm Claudette.

The Kauai event shattered this record without the involvement of a tropical cyclone — just historically high moisture levels over the Pacific  Ocean colliding with unstable air masses streaming down from the north.

Three large bursts

Kauai is the rainiest place on Earth, receiving some 400 inches (10160 mm) of rain per year. It rains on most days, but this single-day rainfall far exceeded the soggy norm. One one day, the total rainfall amount was comparable to about one and a half months of precipitation for the world’s wettest location. Although some precipitation occurred through most of the period, the primary contributors to the very large 24-hour total occurred in three bursts.

Valid measurement

After the event, the TB4 and datalogger were put through several calibration tests using equipment designed or adapted for the purpose of analyzing gauge performance under high rainfall rates. The tests showed that the gauge performed within expected tolerances.