A New U.S. 24-Hour Precipitation Record: 49.69" on Kauai, HI on April 15? by Dr. Jeff Masters

The National Weather Service in Hawaii reported on Wednesday that preliminary data from a rain gauge on the north shore of Kauai at Waipa, one mile west of Hanalei, received 49.69” of rainfall over the 24-hour period ending at 12:45 pm April 15. If verified, this would break the all-time U.S. 24-hour rainfall record of 43.00” in Alvin, Texas set on July 25 – 26, 1979, during Tropical Storm Claudette. The record-setting rains on Kauai were due to an upper-level low located to its west on April 14 - 15, combined with a surge of rich low-level moisture. This set-up brought radar-estimated rainfall rates of 2 – 4” per hour to the north shore of the island.

The National Weather Service office in Honolulu noted that the rain gauge where this new data was downloaded from "is operated by the Waipa Foundation which is a non-profit organization. Data from the gauge are not telemetered for real-time display and are used for watershed modeling and monitoring studies." In the coming months, data from this gauge will be reviewed by the National Climatic Extremes Committee to determine whether this instrument is reliable enough to accept as a new U.S. record.

The April 14 – 15, 2018 event also brought a 25.92” 2-day precipitation total for the perennial Hawaiian wet spot Mt. Waialeale, Kauai, and a 24-hour total of 27.52” to Hanalei, Kauai. Personal weather station KHIHANAL2 in Hanalei recorded 43.49” in the 24 hours ending at 4:18 am April 15, at which time the station stopped sending data. The owner of this gauge noted in their “Status” message, though, that they received 34.73” of rain on April 15, and it is possible that this gauge received a 24-hour precipitation total approaching the 49.69” measured two miles to its west, at Waipa. I contacted the owner of the gauge, and he commented that "having years of experience with the WU, VWS and my WMR200’s I am confident and stand behind my readings 100%. Being a surfer, we follow the weather world wide and especially in Hawaii waters for surf predictions."

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