March 2021 Hawaii floods

The March 2021 Hawaii floods refer to a series of flash‑flooding events that affected the Hawaiian Islands, principally the island of Oʻahu, during the first weeks of March 2021. The storms produced record‑breaking rainfall totals, leading to widespread flooding, landslides, infrastructure damage, and fatalities.

Meteorological background

• On 7 March 2021, a moisture‑laden low‑pressure system, embedded within a broader Pacific storm pattern, moved across the central Pacific.
• The system stalled over the Hawaiian Islands, delivering intense convective activity.
• The National Weather Service (NWS) in Honolulu recorded a 24‑hour precipitation total of 7.71 inches (196 mm) at the Honolulu International Airport, a value approaching the location’s 24‑hour record. Other sites on Oʻahu reported totals exceeding 10 inches (254 mm).
• The heavy rains were accompanied by strong gusts, with wind speeds of up to 45 mph (72 km/h) reported in some coastal areas.

Impacts

Human casualties

• The floods caused at least three confirmed deaths on Oʻahu. Two fatalities resulted from vehicle‑related incidents on flooded roadways, and one death was attributed to a landslide that struck a home in the Puna district.

Infrastructure and property

• More than 1,200 homes and businesses experienced water intrusion, with dozens suffering severe damage requiring temporary displacement of occupants.
• Major roadways, including portions of the Kamehameha Highway (Route 99) and the H-1 freeway, were closed due to floodwaters and debris.
• The Kaka‘ako and Waikiki districts experienced street‑level flooding that disrupted traffic and public transit.

Landslides

• The heavy precipitation triggered multiple landslides, particularly in the windward and central regions of Oʻahu. Notable incidents occurred near the Kamehameha Highway in the Waialua area and on the slopes of the Koʻolau Range, blocking access to several rural communities.

Utilities

• Hawaiian Electric reported power outages affecting roughly 30,000 customers across Oʻahu and Maui.
• Water utilities experienced temporary service interruptions due to damaged pump stations and contaminated supply lines.

Emergency response

State and local agencies

• The Hawaii Department of Emergency Management (HIDEM) activated its Incident Command System and coordinated with the Federal Emergency Management Agency (FEMA) for supplemental resources.
• The Hawaii National Guard deployed over 150 personnel to assist with evacuations, traffic control, and distribution of emergency supplies.

Federal assistance

• FEMA authorized a Disaster Declaration for the state of Hawaii on 10 March 2021, unlocking individual assistance and public assistance funding for recovery operations.

Community actions

• The American Red Cross opened several shelters in Honolulu, Kahului, and Hilo, providing temporary housing, meals, and basic necessities to displaced residents.
• Volunteer groups and local churches organized donation drives for food, clothing, and household items.

Aftermath and recovery

• By late March 2021, most primary roadways had been reopened, though some secondary routes remained closed for repairs and slope stabilization.
• Reconstruction efforts focused on flood‑resilient design, including elevated foundations for homes in flood‑prone zones and improved drainage infrastructure along the windward coast.
• The event prompted a review of Hawaii’s flood‑risk mapping and led to updates of the state’s floodplain management guidelines.

Related events

• The March 2021 floods are part of a pattern of increasingly frequent heavy‑rain events in Hawaii, which also includes the October 2018 wet season floods and the February 2019 floods on the island of Maui.

References

1. National Weather Service Honolulu, “Preliminary Local Storm Report – March 7‑8, 2021.”
2. Hawaii Department of Transportation, “Road Closure and Traffic Impact Report, March 2021.”
3. Federal Emergency Management Agency, “Major Disaster Declaration – Hawaii (DR‑4417).”
4. Hawaiian Electric, “Power Outage Summary – March 2021.”
5. Hawaii Department of Emergency Management, “After‑Action Report: March 2021 Floods.”