Flash Flood — Honolulu, Hawaii

2018-04-13 · near Aina Haina, Honolulu, Hawaii

Event narrative

Traffic stalled in all lanes of Kalanianaole Highway in East Oahu near Niu Valley due to 10-12 inches of standing water on the roadway, and the water was still rising. Moments later, the roadway was closed from Aina Haina to Makapuu due to flooding.

Wider weather episode

A developing upper low northwest of the state, in combination with tropical moisture, induced periods of heavy showers and thunderstorms, and generated historic flash flooding conditions over the Garden Isle of Kauai. An apparent 24-hour rainfall total of 49.69 inches, ending at 1245 HST April 15th, was recorded at an automated rain gauge

in Waipa, Kauai, about a mile west of Hanalei. If this total is certified, it will be a new 24-hour rainfall record for the United States, beating the old record of about 43 inches in Alvin, TX, on July 25-26, 1979.

The deluge, mainly over northern Kauai but also affecting East Oahu, damaged or destroyed farms and various structures, including 532 homes; downed trees and power lines; flooded homes, businesses and vehicles; and closed and damaged numerous roadways with water and debris flows, with highway and road repairs estimated at $35 million. There were apparently no significant injuries, but material losses will be extremely exorbitant, with public property damages alone estimated at $19.7 million. Hawaii's state legislature already approved, as of April 25th, $100 million in relief aid for flood-ravaged communities on Kauai and Oahu. (The aid package was later increased to $125 million.).

View location on OpenStreetMap → (21.2806, -157.7441)

Source: NOAA Storm Events Database, event_id 742752. Narrative written by the NWS forecast office that issued the report.