May 2026 Monthly Rainfall Summary for Hawaii

Monthly Precipitation Summary 

State of Hawaii 

Month: May 2026

Prepared: June 4, 2026

Note: This summary uses the arithmetic mean, or average, for “normal” rainfall values. 

Averages used in this summary have switched to the 1991-2020 values where available.

State: [Text data table for rain gages]

Headline: Typical trade wind weather with a mid-month thunderstorm interlude.

May began with typical moderate to breezy trade winds. A weak upper-level low northeast of the state provided minor enhancement to windward and mauka showers through the 4th, while most leeward areas remained dry.

Trade winds weakened from the 5th through the 10th as the surface ridge relaxed, allowing land and sea breezes to develop. Increased humidity led to afternoon clouds and a few light showers over interior and leeward areas through the 7th. A hybrid pattern of light trades and local breezes continued through the 10th as a weak surface trough moved across the islands, bringing a modest increase in moisture and enhanced windward showers, particularly over the western islands. Moderate to breezy trades returned from the 11th through the 14th, bringing a more typical pattern of scattered windward and mauka showers with occasional spillover into leeward areas.

The most significant weather event of the month occurred on the 15th as an upper-level low moved over the state, creating unstable conditions and enhanced showers statewide. Oʻahu was the primary focus, with scattered heavy showers during the morning becoming more widespread with intense thunderstorms and copious lightning in the early afternoon and into the evening. The heaviest rainfall occurred across central Oʻahu and along the Koʻolau Mountains, where 24-hour totals ranged from 2 to 7 inches with rainfall rates of 2 to 4 inches per hour. Rapid stream rises and flash flooding led to several road closures, particularly in the Waikāne, Waiāhole, Waipahu, and Kunia areas. Pea-sized hail was reported in Mililani as well. Following the departure of the upper low, light to moderate trade winds persisted through the 20th. Lingering moisture supported periods of enhanced windward and mauka showers, with the most widespread rainfall occurring over Maui and the Big Island.

Conditions gradually dried out through the 28th as the atmosphere stabilized and high pressure strengthened north of the state. Trade winds increased into the breezy to locally strong range as typical scattered windward and mauka showers returned, with little rainfall over leeward areas. Winds eased slightly after Memorial Day, though the overall pattern remained unchanged. Trade winds weakened to light to moderate speeds during the final days of the month as the surface high north of Hawaiʻi weakened and shifted farther north. Scattered showers remained focused primarily over windward and mauka areas, while most leeward locations stayed dry.

Island of Kauaʻi : [May 2026 map] [year-to-date map]

The windward and higher elevation focus of the rainfall this month kept those areas above normal for May. The leeward areas missed out on much of the rain, and as such, only got about 40 to 70% of their usual May totals. For the second month in a row, the USGS gage on Mt. Waiʻaleʻale had the highest monthly total for the island and the state with 52.46 inches (170% of average), as well as the highest daily total for the island and the state with 12.60 inches on the 18th. The Līhuʻe Airport (period of record since 1950) broke a daily rainfall record this month with 4.54 inches on 5/15 (old record 1.64 inch in 1962). In addition, two sites had their wettest May in a while: the USGS gages at Kilohana (since 2010) and Mt. Waiʻaleʻale (since 2003).

The year to date (YTD) totals and percentages of average were all near to above average again this month, a few still nearly twice their averages for the year so far thanks to the significant late-winter. The highest YTD total still belongs to Mt. Waiʻaleʻale with 211.21 inches (136% of average).

Island of Oʻahu: [May 2026 map] [year-to-date map]

Windward areas and the higher elevations came in above average again for May, with the leeward areas reporting below average rainfall (mainly 50 to 70%). The usually drier central portion of the island also had above average rainfall for the month, almost exclusively due to the intense storms on the 15th. The USGS Tunnel RG site had the highest total for the month with 23.88 inches, (238% of average). The highest daily total went to the NWS Kunia Substation Ua Net site with 7.40 inches on the 15th. The NWS Kunia Substation and Mānoa Lyon Arboretum Ua Net sites both recorded their wettest May on record (since 1991).

The year to date (YTD) totals continue to run well above average for all reporting stations. The highest YTD total came from the USGS Moanalua RG with 123.96 inches (221% of average). 

Maui County: [Maui May 2026 map] [year-to-date map] [Molokaʻi/Lanaʻi May 2026 map] [year-to-date map]

The trends seen on Kauai and Oahu continue for Maui County. Windward slope locations had above average rainfall in May, while most leeward and interior areas were well below average (around 60% or less). The USGS Puʻu Kukui gage had the highest monthly total in the county with 37.37 inches (134% of average), as well as the highest daily total of 7.43 inches on the 15th. This site also recorded its wettest May since 2005 (caveat of missing data in 2015). 

The year to date (YTD) totals for all reporting sites in the county were near to above average (around 100 to 300%). The highest YTD total was at Puʻu Kukui with 170.63 inches (105% of average. 

Island of Hawaiʻi: [May 2026 map] [year-to-date map]

As with the other islands, the windward coast and upper slope areas fared the best in May, with near to above average rainfall. Much of the leeward coast as well as the leeward Kona and Kohala District slopes came in below average, a handful of which struggled to reach 20% of their May average. The Kaʻū District was dry for the most part, except for a few sites near South Point. The USGS gage at Honoliʻi Stream had the highest monthly total with 38.87 inches (237% of average), as well as the highest daily total of 7.39 inches on the 17th. The USGS gage at Kawainui Stream and the NOAA/CRN site at Waiākea Experimental Station each had their wettest May on record (since 2010). The NWS Ua Net site at Pāhoa Beacon also recorded its wettest May on record (since 1991), with the caveat of missing data in 2016. The Ua Net site at Laupahoehoe PD nearly tied its record wettest May (since 1991), but came in a close second by a few hundredths of an inch. 

The year to date (YTD) totals were mostly near to above average for the island, though the leeward sides are starting to show signs of drying out. The highest YTD total goes to the USGS gage at Honoliʻi Stream with 129.26 inches (135% of average).

Data Sources: Data used in this report are from National Weather Service sources including climate network weather observation stations at Līhuʻe, Honolulu, Kahului, and Hilo, the Ua Net network of automated rain gages, and selected Cooperative Observer sites. Additional data come from automated rain gages operated by the State of Hawaiʻi Department of Land and Natural Resources, the U.S. Geological Survey (USGS), the U.S. Bureau of Land Management, the U.S. National Park Service, the Department of Defense, the U.S. Fish and Wildlife Service, and the U.S. Department of Agriculture, as well as manual observations from the Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS). Averages come from the National Centers for Environmental Information (1991-2020 series) and the Rainfall Atlas of Hawaiʻi (https://www.hawaii.edu/climate-data-portal/hawaii-climate-atlases/). Supplemental data used in some of the analyses are from the Hawaiʻi Climate Data Portal (https://www.hawaii.edu/climate-data-portal/). Data presented here are not certified and should be used for informational purposes only. 

Tina Stall
Senior Service Hydrologist 
NOAA/NWS Weather Forecast Office Honolulu