In April 2018, a series of thunderstorms produced record-breaking rainfall on the Hawaiian Islands of Kauaʻi and Oahu.

There, a rain gauge owned by the Waipā Foundation, just west of Hanalei, recorded 49.69 in (1,262 mm) of rainfall in the 24 hours between 12:45 p.m. on April 14 and 15.

The heavy rainfall produced flash flooding and landslides that covered roads and washed away several vacant houses.

That day, a mesoscale convective system (MCS) developed northwest of Molokai and intensified while moving westward through the trade winds.

After a five-hour break in rainfall, another set of thunderstorms hit northern Kauaʻi around midnight on April 15 and lasted about eight hours.

The flooding knocked down trees and power lines, eroded many bridges and roads, and washed away crops, beehives, and livestock.

[1][3][4][5] Across eastern Oahu, the mesoscale convective system produced rainfall rates of about 4 in (100 mm) per hour.

[1] A rain gauge owned by the Waipā Foundation, just west of Hanalei on Kauaʻi's northern coast, recorded 49.69 in (1,262 mm) of rainfall in the 24 hours ending at 12:45 p.m. local time.

Along the Hanalei River, the United States Geological Survey (USGS) estimated that floodwaters rose 15 ft (4.6 m), representing a peak flow rate of 32,700 cubic feet per second (ft3/s, 926 m3/s) before the station failed.

Landslides occurred at 15 locations along the highway, leaving residents in Wainiha and Haena without regional road access, disrupting relief efforts.

Initially, the declaration was limited to federal reimbursement for repairs to public infrastructure, but on June 27 it was expanded to include individual assistance.

[22] On November 30, Carvalho granted $500,000 to six nonprofits for counselors, meals, emergency supplies, and rebuilding parts of the Limahuli Garden and Preserve.

[25] The Hawaii Department of Transportation ran convoys throughout the day along the damaged portions of Kuhio Highway while it was being repaired.

[17] In August 2018, Hurricane Lane dropped heavy rainfall in the same area, causing further flooding damage to houses and the Kuhio Highway.

[31] On August 2, 2018, National Weather Service Senior Hydrologist Kevin Kodama inspected and calibrated record-breaking rain gauge at Waipā Garden, confirming that the instrument was functioning normally.

On December 4, 2018, the National Climate Extremes Committee verified that the 49.69 in (1,262 mm) accumulation was the highest 24-hour rainfall total in the U.S.[10]