It’s now May and we’ve finally entered the 2026 dry season. The weather has settled into a drier pattern and we’re having an increase in more stable trade wind days. It seems like now is a good time to recap the eventful 2025-2026 Hawaiian Islands hoʻoilo (wet season). By my unofficial count, there were 25 flash flood events across the Hawaiian Islands in the October 2025 through April 2026 wet season. This number of events is the third highest since the 2004-2005 wet season, with 2005-2006 being #1, followed by 2017-2018 at #2 (see graph below). The 2005-2006 wet season included the so-called “40 Days of Rain” from late February through March, while the 2017-2018 wet season had the U.S. record 24-hour rainfall at Waipā, Kauaʻi in April. I imagine the devastating North Shore Oʻahu flooding in March will be the salient event for this wet season, but it was by no means the only one.
Number of flash flood events in the State of Hawaiʻi by wet season. The indicated year is for the January through April portion of the wet season.
Within the wet season there were seven main heavy rain events by my accounting that produced most of the flood impacts. They are:
- December 14-20, 2025
- January 4-6, 2026
- February 7-10, 2026
- February 20-21, 2026
- March 11-15, 2026
- March 19-23, 2026
- April 7-12, 2026
The wet season actually got off to a slow start with October and November being generally dry. As mentioned in previous posts, this is consistent with recent trends. The December 14-20, 2025 event was the first significant heavy rain event of the season. The main impacts occurred early-on with urban flooding over Oʻahu on December 14. This was the same day as the Honolulu Marathon so the storm created rather soggy running conditions. The Multi-Radar/Multi-Sensor (MRMS) radar reflectivity mosaic below from December 14 shows a southwest-to-northeast rain band draped over the southeast half of Oʻahu that produced the urban flooding issues.
Composite reflectivity mosaic for 1 PM HST, Sunday, December 14, 2025 from the NOAA National Severe Storms Lab’s Multi-Radar/Multi-Sensor (MRMS) system website. The image from the website was cropped for visual clarity.
Shortly after the New Year holiday, a low pressure system threatened the state with heavy rain and flash flooding conditions. Fortunately, the January 4-6, 2026 event ended up producing the highest rainfall totals of 10 to 13+ inches mainly over the east side of the Big Island (see figure below), which can generally handle quite a bit of rainfall, especially if the rain rates stay at or below the 1 to 2 inch per hour range. From what I saw, the closure of Highway 11 at a location known as “Kāwā Flats” south of Pāhala was the only significant flash flood impact during this period.
Map of gridded rainfall in inches for the 3-day period from January 4th through 6th, 2026. The data come from the HCDP daily rainfall data grids.
These first two events were just warm-up swings. Starting in February and continuing through March is when the “fo’ real stuff” started happening. The first of the big events hit the state on February 7-10 in what I called the “Super Bowl Sunday” storm. Even though the 4-day rainfall totals were impressive, rain rates were generally manageable and limited the amount of flash flood impacts. Ultimately, this was more of a destructive wind storm than a significant flash flood-producing system. Blaster trade winds hit the state, with localized terrain interactions causing extreme wind gusts over 60 miles per hour in several areas. The map below shows gusts over leeward West Maui reaching 83 miles per hour, or greater than hurricane force (74 miles per hour). These winds produced numerous incidents of downed trees and powerlines, and structural damage to homes and businesses.
Map of peak gusts for February 9th, 2026 on Maui. All values are in mph. The maps are from the National Weather Service’s Weather and Hazard Data Viewer.
A couple of weeks later, on February 20th and 21st, the most intense rain event of the wet season hit windward Oʻahu. A negatively tilted low pressure trough aloft produced conditions favorable for thunderstorms and intense rainfall. The interaction of the low level winds with Oʻahu’s complex terrain may have helped anchor storms to the same location for a prolonged period. The storm produced over 17 inches of rain in a 6-hour period at the Luluku rain gage located on the grounds of the Hoʻomaluhia Botanical Garden near Kāneʻohe, Oʻahu. The MRMS loop below shows heavy rainfall (orange and red colors) occurring along most of the Koʻolau Range, but the most intense core over and around Kāneʻohe remains nearly stationary.
Seamless Hybrid Scan Reflectivity loop from 5 AM to 9 AM HST, Saturday, February 21, 2026 in 10-minute time steps from the NOAA National Severe Storms Lab’s Multi-Radar/Multi-Sensor (MRMS) system website. The images from the website were cropped for visual clarity.
March ended up being the peak of the wet season with the highest number of flash flood events (16) and the most rainfall across the state. It included the largest rain event (March 11-15) in terms of storm totals, and the most impactful (March 19–23) in terms of fatalities and losses from flood damage. I called the March 11-15 kona low a “once in a generation” storm because it was the most impactful non-tropical cyclone storm system to affect the state since the large kona low in January 1980. With 30 to nearly 50 inches of rain in a 5-day period, it was the largest storm system in terms of rainfall totals for the 2025-2026 wet season. It did not appear to have the most intense rainfall (see February 20-21 storm above), but its longer duration totals were on the extreme end of the frequency distribution curve with annual probabilities of less than 0.1% (>1000 year return period!). The Kīhei area of Maui and the Kona side of the Big Island were hit especially hard by flooding. The GOES-18 satellite loop below shows multiple rain bands moving across the state over several days. Strong winds with numerous reports of gusts above 60 miles per hour knocked down trees and utility poles and caused property damage in several areas across the state. A Hawaiʻi Mesonet station at Kaiāulu Puʻu Waʻawaʻa (Kona side of the Big Island) recorded a peak wind gust of 135.4 miles per hour (Hawaiʻi Climate Data Portal Instagram post, March 20, 2026).
Loop of color enhanced infrared (IR) images from the Himawari-9 satellite covering the period from 2 PM HST March 9 to 2 AM HST March 15. The images come from the RAMMB/CIRA SLIDER archive and are spaced 12 hours apart. The main Hawaiian Islands are within the red oval at the start of the loop.
Just a week later, while residents were still recovering from flood and wind impacts, another storm system hit the state on March 19-23. It wasn’t the highest rainfall producer of the wet season, but it did show that hydrologic factors are often more important than meteorological factors in determining flood impacts. Yes, there was intense rainfall, but in this event, the saturated soils from earlier rainfall made the flooding response over the same areas much worse than the previous week. The figure below shows the North Shore region of Oʻahu that received the most devastating flooding from this event.
Multi-Radar, Multi-Sensor (MRMS) radar and rain gage rainfall estimates for the 12-hour period ending at 5 AM HST, March 20, 2026. Light blue lines are streams, and the red line outlines the Kiʻikiʻi/Kaukōnāhua drainage basin. Stream lines and the basin boundary are from the Hawaiʻi Statewide GIS Program and the Wahiawā Dam location is from the U.S. Geological Survey’s Pacific Islands Water Science Center.
The final flash flood event of the 2025-2026 hoʻoilo occurred on April 7-12, 2026. Compared to earlier events in the season, this event did not produce serious impacts even though there were still some impressive storm rainfall totals. The figure below shows the 6-day accumulated rainfall across the main Hawaiian Islands, with the highest amounts of more than 15 inches over the lower Kaʻū and Puna slopes on the Big Island. The Kealakomo gage recorded 11.94 inches in a 6-hour period (500-1000 year return period) but there were no known flood impacts in the area. This also illustrates the importance of hydrologic factors. In this case, it’s soil type and land use. Young, porous lava soils and no urbanization on the lower slopes of the Puna District result in minimal runoff.
MRMS 6-day accumulated precipitation covering April 7th through April 12th, 2026. The data in this graphic were downloaded from the MRMS repository on the Registry of Open Data on AWS and processed using QGIS software.
The table below shows the top three rainfall amounts during the October 2025 through April 2026 wet season for various durations from 1-hour to 24-hours. The date/time column refers to the end of the specified duration. The data are from the Hawaiʻi Mesonet, the HADS website, and the Western Region Climate Center’s RAWS data archive. Return periods for each site are from NOAA Atlas 14.
The highest amounts for the shorter term durations (1- through 6-hours) are dominated by the Luluku and Moanalua Rain Gage sites on Oʻahu from the February 21 intense rain event. The longer durations are dominated by rainfall from the kona low on March 11-15. Once state officials tally all the impacts, it may end up being the costliest wet season on record in terms of damage dollars. This may hold true even after accounting for adjusted dollar amounts for events in prior years/decades. The 2005-2006 hoʻoilo is still worse in terms of fatalities because of the 7 deaths on Kauaʻi from the Kaloko Dam failure.
| Station, Island | Inches | Return Period (yrs) | Date/Time |
| 1-hour duration | |||
| Luluku, Oʻahu | 5.38 | 200-500 | 21 Feb 26/7:45a |
| Moanalua RG, Oahu | 4.76 | 25-50 | 21 Feb 26/10:00a |
| Honokaʻa, Big Is | 4.55 | 200-500 | 7 Feb 26/6:30p |
| 3-hour duration | |||
| Luluku, Oʻahu | 13.01 | >1000 | 21 Feb 26/10:00a |
| Moanalua RG, Oʻahu | 12.49 | 500-1000 | 21 Feb 26/10:15a |
| Kamananui RAWS, Oʻahu | 8.30 | 500 | 20 Mar 26/2:00a |
| 6-hour duration | |||
| Luluku, Oʻahu | 17.07 | >1000 | 21 Feb 26/10:00a |
| Haleakalā Summit, Maui | 14.00 | >1000 | 14 Mar 26/12:35a |
| Moanalua RG, Oʻahu | 13.44 | 200 | 21 Feb 26/10:15a |
| 12-hour duration | |||
| Haleakalā Summit, Maui | 21.99 | >1000 | 14 Mar 26/5:15a |
| Luluku, Oʻahu | 21.72 | >1000 | 21 Feb 26/2:45p |
| Kula 1, Maui | 19.62 | >1000 | 14 Mar 26/5:48a |
| 24-hour duration | |||
| Haleakalā Summit, Maui | 33.15 | >1000 | 14 Mar 26/8:35a |
| Kula 1, Maui | 31.43 | >1000 | 14 Mar 26/5:48p |
| Nāhuku, Big Is | 28.57 | >1000 | 14 Mar 26/10:45p |