Tropical Storm Lala: Hawaii Rainfall Records & Flooding Projections

Although Tropical Storm Lala is officially moving away from the Hawaiian Islands, meteorologists and local authorities are still unpacking the sheer volume of precipitation dumped over the weekend.

The storm produced historically heavy rainfall, peaking at over 1,090 millimeters in the mountains of the Big Island (Hawaii) and up to 610 millimeters in Maui. These extreme volumes caused flash flooding, major mudslides, and catastrophic infrastructure collapses across the state.

To put these numbers into context, we’ve built a converter and runoff simulator to calculate how these figures translate to standard measurements.

Rain Volume & Runoff Calculator

Convert rainfall metrics from millimeters to inches, and calculate the estimated runoff volume (in gallons per acre) based on the rainfall totals:

Pahala Highway Collapse and Infrastructure Damage

The catastrophic rainfall led to a massive failure of the Pāhala highway in the southeastern portion of the Big Island. Over 1,000 mm of rain filled the Pa’au’au stream, causing it to breach a retaining rock wall and spill directly onto the road.

The resulting high-velocity water flow completely washed out sections of the highway, creating a new waterfall and tearing down several small bridges. This road collapse has effectively cut off access to a crucial regional hospital, leaving up to 2,500 residents completely isolated.

Power Outages and Cleanup Efforts

Beyond the flooding, the storm brought wind gusts matching Category 1 hurricane force (which Lala temporarily became on Saturday before weakening).

These winds knocked down power lines and uprooted trees across Hawaii, Honolulu, and Maui counties, leaving more than 120,000 customers without electricity. The Hawaii National Guard has deployed heavy machinery to assist local crews in clearing roadways.