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 April 14 to 15, 2018. In 24-hours to 12:35 HST, April 15, Waipa Garden in Kauai recorded 1 262.1 mm (49.69 inches) of rain, breaking the previous 24-hour record precipitation for the United States of 1 092.2 mm (43.00 inches) registered on July 25/26, 1979 at Alvin, Texas.
During the two-day period spanning the calendar dates April 14 - 15, 2018, the station recorded 1 380.99 (54.37 inches) of rainfall. The greatest 24-hour total from the 15-minute incremental observations was 1 262.12 (49.69 inches), for the 24-hour period ending 12:45 HST, April 15, 2018. Although some precipitation occurred through most of the period, the primary contributors to the very large 24-hour total occurred in three bursts, spanning roughly:
- 13:00-19:00 HST on the 14th, when just under 508 mm (20 inches) of rain was recorded
- 00:00-05:00 on the 15th, when about 457.2 mm (18 inches) of rain was recorded
- 10:30-12:45 on the 15th, when about 203.2 mm (8 inches) of rain was recorded
Regionally, April 14 - 15, 2018 was marked by several ingredients conducive to very heavy rainfall.
A warm, unstable surface layer and deep moisture prevailed across the region. An upper level low west of the Hawaiian Islands, combined with a subtle mid-level trough nearer to Kauai, acted to further destabilize the atmosphere.
This, combined with the absence of any notable inversion layer in the region, further enabled deep convection as a mode of precipitation. Breezy trade wind flow advected moisture to and through the region, maintaining a supply of warm, moist surface air to fuel convection.
Any national or state record precipitation value is by nature unanticipated. However, heavy rain, with embedded deep, sustained convection, was anticipated and observed across much of Kauai during the 14th and 15th. Flash flood warnings were numerous, and significant to catastrophic flooding was documented across much of the island.
You can learn more about the effects of this rain at the following link:
Record-shattering rains trigger destructive floods in Hawaii (April 16, 2018)
The previous U.S. 24-hour precipitation record was 1 092.2 mm (43 inches), near Alvin, Texas, on July 25 - 26, 1979, in association with the 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.
Featured image: Home destroyed by flash floods in Hawaii on April 14, 2018. Credit: Kresta Kay