In early November 2000, thunderstorms on the island of Hawaiʻi produced torrential rainfall, flash floods, and landslides. The weather event was from the interaction of an upper-level trough and the remnants of Tropical Storm Paul, a short-lived tropical cyclone in the eastern Pacific Ocean. The contrasting weather forces produced strong thunderstorms along the mountainous slopes of Hawaiʻi, beginning on October 28 and lasting until November 3. The highest precipitation was 38.97 in (990 mm) at Kapapala Ranch near Pāhala. This included 37.02 in (940 mm) measured over 24 hours. The latter observation was the highest 24 hour rainfall total on record for the island. The floods damaged or destroyed four bridges along the Mamalahoa Highway, and another three bridges in Hilo, isolating several neighborhoods. Overall damage totaled $88.2 million (2000 USD). The damage led to a state of emergency and a federal disaster declaration.

Meteorological history

On October 22, 2000, the Intertropical Convergence Zone produced an area of convection off the southwest coast of Mexico in the eastern Pacific Ocean. Moving to the west, it organized into Tropical Depression Eighteen-E on October 25. Despite the presence of wind shear, the depression strengthened into a tropical storm on October 26, named Paul by the National Hurricane Center (NHC). Soon after, Paul attained peak winds of 45 mph (75 km/h), although it weakened soon after with only intermittent convection. On October 28, Paul weakened to a tropical depression. That day, heavy rainfall began affecting the island of Hawaiʻi. Although Paul's circulation dissipated on October 29, moisture from the storm interacted with an upper-level trough about 500 mi (800 km) southwest of Kauai. The interaction of the warm tropical air with cooler air aloft, in addition to the direction of the tradewinds and the mountainous terrain, created favorable conditions for thunderstorm development.

From October 28–29, strong thunderstorms affected eastern Maui, producing heavy rainfall totaling 24 in (610 mm). The heaviest rainfall occurred from November 1–2 on the island of Hawaiʻi. At Kapapala Ranch near Pāhala, a rain gage recorded 38.97 in (990 mm) of rainfall, the highest amount in association with the event. The station also recorded 22.25 in (565 mm) over six hours, and 37.02 in (940 mm) over 24 hours. The latter observation was the highest 24 hour rainfall total on record for the island. It was also within 1 in (25 mm) of the then-highest 24 hour–rainfall total in the state of Hawaii, set on January 25, 1956. Several areas across the island of Hawaiʻi recorded 1 in 100 year precipitation events. Other significant rainfall totals included 32.47 in (825 mm) recorded in Mountain View, of which 29.75 in (756 mm) fell in 24 hours. Hilo International Airport recorded 4.56 in (116 mm) in one hour, and 26.89 in (683 mm) over 24 hours. The Hilo daily rainfall total broke the record set in February 1979 by more than 4 in (100 mm). Additionally, 16.2 in (410 mm) was recorded on November 2, which set the new calendar day total for the month of November, surpassing the previous total of 15.4 in (390 mm) on November 18, 1990. The rains led to flash flooding that collected in streams and carved out new flood channels. The floods also generated several landslides, some of which affected the Hawaii Belt Highway. Along the Wailuku River near Hilo, a gauge recorded a peak flow of 75,000 ft3 per second (2,123 m3 per second). Four gauges recorded record flows, including the Alenaio Stream, which produced floodwaters 10 ft (3.0 m) deep. The rainfall continued until November 3.

Impact

Rainfall totals on the island of Hawaii

On the island of Maui, the thunderstorms produced flash flooding along the slopes of Haleakalā. Runoff flowed over bridges and parts of the Hāna Highway. Several drivers and tourists required rescue from police. The floods also closed or damaged several roads, including some affected by large boulders. The floods also impacted the island of Molokaʻi, with ten homes damaged. A man in a flooded vehicle required rescue in Puko'o. Water levels reached 13 ft (4.0 m) in Waialua.

The flooding left $88.2 million in damage to the island of Hawaiʻi. Most of the cost was infrastructure, with 71% of the overall damage related to roads, bridges, and drainage systems. The most affected districts were Hilo, Ka’u and Puna. Across Hawaiʻi, the floods damaged or destroyed 298 residences. Four people required rescue, and dozens of families evacuated their homes. The floods damaged or destroyed four bridges along the Mamalahoa Highway, the only direct connection between Hilo and Pāhala. In Hilo, the floods washed out two bridges over Waiakea Stream and one bridge over Alenaio Stream. Several Hilo neighborhoods were isolated and only accessible by boat or helicopter. Schools and businesses across the island closed due to the floods. In Hilo, the Alenaio Stream uprooted trees and damaged bleachers. The stream's floods were limited due to a soccer field serving as a catch basin, as well as a floodwall built by the United States Army Corps of Engineers in 1997. The 2000 flood tested the project, and was estimated to have prevented $20 million in damage. The flooding also damaged businesses and public facilities.

Aftermath

Flooding along the Alenaio Stream on the Big Island of Hawaii

Due to the damaging floods, then-Governor Ben Cayetano declared a state of emergency on November 3. The governor activated the National Guard, which assisted with evacuations, debris removal, and delivering supplies. The American Red Cross provided shelter, food, and clothes. The Hawaii State Civil Defense set up a Disaster Recovery Branch to help county officials manage the disaster. Within a week of the floods, construction crews built a temporary 11.5 mi (18.5 km) gravel road to bypass the damaged Mamalahoa Highway. Repair costs to state and county infrastructure totaled $4.5 million.

On November 9, then-President Bill Clinton declared the island of Hawaii as a disaster area, allowing residents to request for assistance. Federal Emergency Management Agency (FEMA) and Hawaii State Civil Defense opened disaster recovery centers in Hilo and Pahala to provide the affected people with information about disaster assistance programs. Ultimately, more than $4.1 million was spent in public assistance. These included $1.4 million for temporary housing and $2.3 million in direct grants. The Small Business Administration provided $5 million loans to small businesses and another $2.5 million to farmers. Overall, federal disaster assistance totaled $88 million for Hawaii, due to the flooding event.

The county government of the Big Island spent $8.7 million (2000 USD) in repairs, primarily to bridges and flood controls.

Following the floods and additional flood damage in 2008, the Army Corps of Engineers repaired the Alenaio Stream channel and nearby levees.

See also

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