Historic rainfall exposes 1960s infrastructure designed for 100-year storms that arrived twice in three weeks
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As a historic Kona low, a type of seasonal cyclone, clears the Hawaiian Islands, Maui County engineers are assessing damage the Hawaii Dept. of Transportation preliminarily estimates at roughly $23 million statewide—about $7 million on Maui alone—the Honolulu Star-Advertiser reported.
The storm, which began battering Maui County on March 11, drew its destructive force from an atypical southwesterly moisture feed characteristic of Kona lows: slow-moving, upper-level low-pressure systems that can produce extreme rainfall from directions that Hawaii’s drainage infrastructure was never designed to handle.
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The National Weather Service Honolulu reported five-day rainfall totals topping 44 in. in Upcountry Maui, shattering records dating to 1951. Wind gusts of over 70 mph were recorded in Kaunakakai on Molokai, also part of Maui County. The storm struck ground already compromised.
“Prior to this storm, we had three other storms that already affected the islands by pre-wetting, by hitting our vegetation,” HDOT Director Ed Sniffen told the Star-Advertiser. Maui County Mayor Richard Bissen signed an emergency proclamation March 10; Gov. Josh Green (D) subsequently declared a statewide emergency, according to the Office of the Governor.
Footings, Abutments and the Scour Threat Below
Stormwater collapsed road sections and ruptured sewer and water lines in Kihei, Maui Emergency Management Agency (MEMA) Deputy Administrator Kono Davis said. The Hana Highway—one of the world’s most celebrated coastal drives—was reduced to one lane after multiple blockages, HDOT confirmed, and Honoapiilani Highway was closed for a formal bridge integrity assessment.
The Iao Stream Bridge, which drew public concern during the storm, was inspected and cleared, with a visible crack traced to expansion joints documented in its 2024 biennial inspection rather than new storm damage, HDOT said.
Hana lost power and was temporarily isolated by landslides, county officials said, and a water main break in Upper Kula required emergency deployment of portable tanks for drinking water.
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Post-storm, HDOT engineers conducted bridge inspections statewide focused on scour—the erosion of streambed material around bridge footings and abutments driven by high-velocity floodwater—which the department identifies as a primary structural threat to bridges during flood events.
A 5-day cumulative rainfall forecast issued by the National Weather Service Honolulu on March 11, 2026, shows Maui County among the hardest-hit areas, with peak rainfall projected for Thursday night through Saturday. Actual totals exceeded forecast levels, with NWS recording more than 44 in. in Upcountry Maui over five days.
Graphic courtesy National Weather Service Honolulu/NOAA
Inspectors assessed debris lines, checked for stream bed changes and looked for evidence of structure movement or settlement, HDOT said. At the storm’s peak, crews on Maui were temporarily pulled from work sites after winds became strong enough to snap trees around them, Sniffen told The Garden Island newspaper.
Sniffen said the agency’s emergency triage protocol prioritizes ports and airports first as critical aid entry points, followed by hospitals and emergency routes, then the broader highway network. The infrastructure threat extended beyond roads and bridges.
Flooding struck along a deepened fault line exacerbated by deadly wildfires that ravaged the town of Lahaina in August 2023, when at least 102 people were killed and more than 2,200 structures were destroyed. The Lahaina fire remains the deadliest U.S. wildfire in more than a century. Stormwater resilience was already listed as an unfinished priority in the county’s December 2024 Long-Term Recovery Plan, according to MauiRecovers.org—and that gap was exploited March 14 when retention basins overtopped, threatening temporary recovery housing.
Sediment washing down from unstabilized slopes above the community, compounding the risk to life and property, according to local media. An outside contractor was brought in to draw down basin water levels overnight—but county officials acknowledged the vulnerability remains until the recovery plan’s stormwater upgrades are built.
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‘All of That Is More Expensive’
The storm has forced a broader reckoning with Hawaii’s design standards. Many of the state’s drainage systems, bridges and roadways were built in the 1960s and sized for weather patterns that no longer reflect present-day conditions, Sniffen told the Star-Advertiser.
A crack visible on the Iao Stream Bridge in Central Maui drew public concern during the March 2026 Kona low.
Photo courtesy Hawaii Department of Transportation
Those systems were designed for a 100-year storm—a severe rainfall event with a 1% probability of occurrence in any given year.
«You can see, this storm is a 100-year storm, and we had one just three weeks ago,» Sniffen said. Future projects will likely need to be engineered for 200-year or 250-year events, requiring larger drainage openings and bridge clearances. «All of that makes sense,» Sniffen added, «but all of that is more expensive.»
The Hawaii Emergency Management Agency and Maui County officials said damage assessments remain active, with revised figures expected in the coming weeks. Hawaiian Electric, the state’s primary electric utility, reported more than 26,000 customers statewide remained without power as of the evening of March 15, with restoration efforts ongoing, according to a HECO news release.
