The massive downpour in Hawaii in early 2026 resulted in more than two trillion gallons of rain falling on the islands. This amount is enough to fill approximately 3 million Olympic-sized swimming pools.
It made March 2026 the third-wettest March since records began in 1920.
Statewide rainfall averaged 18.25 inches (from March 1 through March 23), or 2.6 times the monthly average of 6.85 inches.
Some areas recorded 14-day rainfall totals up to 3000 percent above normal for this point in the year.
The prolonged rains were generated by back-to-back Kona lows and culminated in a rain bomb producing 2 to 4 inches of rain per hour.
The first Kona low brought record winds to Haleakalā
This storm occurred between March 10 and March 16. Winds associated with the first system reached extreme hurricane-force values, including a maximum gust of 135.4 mph.
At higher elevations on the Big Island, wind speeds were brief but equal to those seen in a Category 2 hurricane.
Peak amounts of rainfall exceeded 60 inches in parts of Maui. Upper slopes of Haleakala Mountain received 33.2 inches of precipitation in a 24-hour period from the late morning of March 13th.
This amount exceeds NOAA’s officially estimated value for a 1,000-year 24-hour extreme rainfall event.
A second Kona low developed between March 19 and March 23. It produced up to 61 inches of rainfall in local areas and catastrophic flooding along eastern and central Molokaʻi, west Maui and Oʻahu.
Communities along the north coast of Oʻahu, including Waialua and Haleiwa, were severely flooded due to torrential rains.
Flooding was reported across multiple islands.
Measured over two consecutive days, the Kaʻala Station reported the highest total for Oʻahu during that storm at nearly 22 inches. The Kalaheʻe Ridge Station above Waimea Valley reported 9.75 inches in 24 hours.
The second storm hit before the rain bomb struck Mānoa
Just before ending the prolonged two-week period of heavy rainfall, a severe localized weather event occurred in Mānoa and Palolo Valleys on March 23rd. As described by Honolulu Mayor Rick Blangiardi, this was a “classic rain bomb,” caused by a stationary storm cell producing heavy rain.
Heavy rain rates of 2 to 4 inches per hour occurred.
Rainfall totals ranged from 3.5 to 6.5 inches at six stations operated by the Hawaiʻi Mesonet in the Nuʻuanu-Mānoa area, where most of that total occurred over a three-hour span.
The University of Hawaiʻi documented additional rainfall and flooding data during the storm.
Due to saturation conditions present throughout the prior week’s storms, lower-than-normal totals of precipitation were required to initiate runoff.
Runoff occurred rapidly, producing flash floods. One example included a rapid rise of the Mānoa Stream causing flooding of adjacent parking lots, streets, and an elementary school.
The Mesonet captured what radar could not
Data used for measurement purposes were gathered from Hawaiʻi’s Mesonet and Climate Data Portal, a growing network of 77 weather observation stations across the state. Due to the presence of mountainous terrain within the state, gathering weather information is difficult because of radar blind spots.
Installing rain gauges in remote locations can also pose difficulties, while wind speeds vary greatly based on elevation and topographic location.
Forecasting challenges increased as well due to the loss of functionality of the Molokai radar during portions of the storm-related flooding.
Built to fill critical weather gaps
In an interview regarding the development of the Mesonet project, Dr. Thomas Giambelluca stated that the goal was to “fill in those spatial gaps and provide data… particularly during extreme events.” He emphasized that collecting this type of data would improve forecasting and assist emergency management personnel following severe events.
Although radar was unavailable on Molokai during portions of the storms, localized rainfall data were collected every five minutes.
These measurements supplied forecasters with information that was otherwise unavailable across parts of the islands.
Read the whole thing?
Get the week's signal, not the noise
Our sharpest reporting on energy, climate and nature — free, once a week.
