UH: Hurricane Lala douses Hawaiʻi with 1.9M Olympic-size pools of water

Almost two million Olympic-size pools of water (1.3 trillion gallons) inundated Hawaiʻi on Aug. 14-16, as Hurricane Lala tracked just south of the islands, according to researchers with the University of Hawaiʻi.

Delivering one of the state’s most significant tropical cyclone impacts in decades, the storm triggered severe flash flooding and damaging winds. Through the University of Hawaiʻi’s Hawaiʻi Mesonet and the Hawaiʻi Climate Data Portal (HCDP), researchers captured the massive scale of this storm.

Lalaʻs impacts brought average statewide rainfall of 11.4 inches. Hawaiʻi County received 66% of the total rainfall volume—equivalent to 1.2 million pools (833 million gallons). 

Nāʻālehu flash flooding and station records

Communities such as Nāʻālehu on Hawaiʻi Island experienced devastating inundation from flash flooding. Hawaiʻi Mesonet stations highlighted the extreme localized intensity of the storm: the Laupahoehoe station in Hamakua recorded a daily maximum rainfall of 32.1 inches on August 15. Almost simultaneously, the Kaiholena station, located upslope of the Nāʻālehu area, recorded 24.4 inches, including a remarkable 4.4 inches of rain in a single hour, 7:30–8:30 p.m. This was the highest observed hourly rainfall rate in the state during the entire three-day event. Combined with steep mountain slopes, this intense rainfall resulted in flash flooding that severely impacted the community in Nāʻālehu.

As the storm progressed, the rest of the counties experienced their peak rainfall a day later, on August 16. While their totals were lower than Hawaiʻi Island’s, they still saw substantial averages: Maui County recorded a cumulative 6.6 inches of rain, equivalent to 203,595 pools (134 million gallons). Honolulu County (Oʻahu) recorded 5.5 inches of rain, equivalent to 86,357 pools (57 million gallons), and Kauaʻi County recorded 3.1 inches, equivalent to 45,055 pools (29 million gallons).

“Storms like Lala remind us why sustained, high-quality rainfall measurement matters so much in Hawaiʻi,” said Tom Giambelluca, director of the Hawaiʻi Mesonet. “Our terrain can turn the same storm into a 2-inch event in one valley and a 40-inch event a few miles away—without a dense network like the Mesonet, we’d have no way to capture that difference or understand what actually happened on the ground.”

Strong winds and dangerous gusts 

The storm also unleashed high winds, with station-derived hourly wind speeds peaking at 60 mph on Hawaiʻi Island. Strong winds were also measured on Maui (56 mph), Oʻahu (39 mph) and Kauaʻi which led to downed power lines and fallen trees across the islands. Wind gusts of 80 mph were recorded at Puʻuloa in Kohala, and up to 79 mph on Haleakalā. Researchers expect that wind gusts were even more intense in some areas that do not have a climate station. 

“One of the biggest challenges with wind is that we simply don’t have stations everywhere, especially at higher elevations and in remote terrain,” said Matt Lucas, HCDP product development lead. “Newly developed high-resolution wind speed maps let us estimate conditions in the gaps between stations, especially in extreme terrain where winds can be accelerated 2–4x by landscape effects. This means disaster responders, property owners, and land managers aren’t left guessing about what happened in places where we didn’t have a station.”

The Hawaiʻi Mesonet, a statewide network of state-of-the-art weather stations, provides critical weather information across the islands giving a birds eye view into the data behind extreme weather events. Using observations from the Hawaiʻi Mesonet and digital maps produced on the HCDP maps, the team has released a new interactive website documenting the weather impacts of Hurricane Lala. Visit the HCDP Extreme Event Page to explore new interactive rainfall and wind speed maps as well as station data from the event. End users can sort information by county and for each day of the storm.