Heavy rains and convection across eastern and northern parts of the island of Kauai, Hawai‘i resulted in multiple reports of very heavy rainfall and flooding on 14-15 April 2018.
The following observation came to light in the days immediately following the event. It was examined by the National Climate Extremes Committee (NCEC) to determine its validity and potential status of the greatest 24-hour rainfall total directly observed in the United States:
• Location: Waipā Garden, Kauai, Hawaii • Date / Time: The 24-hr period ending 1245 HST 15 April 2018
• Amount: 49.69”
After considering the observation and the various surrounding factors, the NCEC determined the Waipā Garden observation to be valid, and it now stands as the 24-hour record precipitation for the United States. This value supersedes the previous record of 43.00” occurring 25-26 July 1979 at Alvin, Texas.
The previous U.S. 24-hour precipitation record was 43 inches, near Alvin, Texas, on 25-26 July 1979, in association with landfall of Tropical Storm Claudette. This rainfall record, already familiar to the applied climatology community, was established by the NCEC when originally constituted in 2000.
As is the case with the Waipā Garden observation, the Alvin observation was recorded by an unofficial observer, but one known to and trusted by the local NWS forecast office. This event was variously memorialized as 42” (the value adopted by the Texas State Climate Extremes Committee) and 43” (as adopted by the National Climate Extremes Committee).
The cause for the discrepancy is unknown. It is possible that the additional inch accounts for rainfall lost to observation during periods when the observer’s direct-read rain gauge overflowed its 10” capacity.