16.63 Inches of Rain Fell in 24 Hours in East Maui — Beats 40 State Rainfall Records But Not Hawaiʻi’s

The storm that dumped buckets of rain on East Maui Monday, causing flooding, evacuations and the Kaupakalua Dam to overflow, was called a “run-of-the-mill low-pressure system for the Hawaiian islands” by an AccuWeather meteorologist.

For the 24-hour period ending at 8 am today, the most rainfall on Maui was recorded at 16.63 inches for the watershed area of West Wailua Iki, near Keʻanae, according to data from the US Geological Survey and reported by the National Weather Service.

While 16.63 inches in one day is a lot of rainfall, it is nowhere near the extreme 24-hour rainfall record for the state of Hawaiʻi. The record is 49.69 inches, set April 14-15, 2018 at Waipā Garden on Kauaʻi, according to data from the National Oceanic and Atmospheric Administration (NOAA).

The 49.69 inches also is a United States record. It exceeded the previous national record of 42 inches set in Alvin, TX, in 1979 during Tropical Storm Claudette. And it exceeded the previous Hawaiʻi record of 38 inches, observed at Kauaiʻi’s Kilauea Sugar Co. Plantation on 24-25 January 1956. That figure was an estimate, according to NOAA.

For those interested in the world record for rainfall in a day, it belongs to the French island territory of La Reunion in the Indian Ocean with an incredible 71.85 inches during Tropical Storm Denise in 1966, according to the World Meteorological Organization.

But, the 16.63 inches just recorded at West Wailua Iki is more precipitation than the extreme 24-hour rainfall record for 40 US states. All the state records can be viewed at NOAA’s National Climate Extremes Committee report.

The two other areas of Maui with the highest recorded 24-hour rainfall, ending at 8 am today, were Puʻu Kukui with 9.31 inches and Haʻikū with 7.57 inches.

Even the 9.31 inches in Puʻu Kukui would better the 24-hour rainfall records of six states: Idaho (7.17), Nevada (7.78), North Dakota (8.1), South Dakota (8.74), Utah (5.08) and Wyoming (6.06).

AccuWeather meteorologist Max Gawryla explained the recent storm this way: Hawaiʻi typically sees mainly trade winds over the region caused by high pressure off to the north. But Monday there was low pressure north of the area that dragged more southeasterly winds across the region, which dragged a ton of very moist air to the islands. When the moist air hit the mountains it lifted up and turned into pretty widespread heavy rain.

Will Ahue, a National Weather Service meteorologist in Honolulu, said the large amounts of rain were due to the storm system moving over the area and then just “sat.”

Cheryl Hendrickson, who lives in Haʻikū and is at higher elevation than the nearby dam that crested, said she was lucky that the heavy rains only flooded her yard and not her house. She said the rain also caused the washout of a section of Awalau Road that is in a gulch near her home.

“I’ve been living up here 14 years and the first 5 to 10 years we’d have at least a month of heavy rain and the area handled it,” she said. “But yesterday, when it kept coming down I became a little concerned to see a river flowing by. It’s never been like that before.”