September 2026 Monthly Rainfall Summary for Hawaii

Monthly Precipitation Summary 

State of Hawaii 

Month: September 2026

Prepared: October 7, 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.

Headline: September was an unusually active month, with two hurricanes, Lowell and Nolo, bringing periods of heavy rainfall, strong winds, flooding, and significant coastal impacts to the Hawaiian Islands.

State: [Text data table for rain gages]

The month began with breezy trade winds as a surface high remained far north of the state and Hurricane Lowell moved westward well to the south. Moisture associated with a passing surface trough helped fuel 1 to 4 inches of rain along windward slopes and higher terrain of most islands through the 2nd. Drier air initially moved in behind the trough, but increasing moisture in the trades led to widespread windward showers on the 5th and 6th. As winds shifted more out of the southeast during this time, terrain interactions produced periods of heavier rain, with two-day totals generally reaching 2 to 6 inches, with locally higher amounts for Maui and Oʻahu. In the Waiāhole/Waikāne area of Oʻahu, rapid rises in the Waikāne and Waiāhole Streams resulted in up to 2.5 feet of water covering Kamehameha Highway, forcing its closure.

The most significant event of the month occurred as Hurricane Lowell approached Kauaʻi and Niʻihau from the south, passing just west of Niʻihau during the night of the 7th as a Category 2 hurricane. Lowell brought hurricane-force southeast to south winds, damaging storm surge, and high surf to the western islands. Kauaʻi experienced major damage from both the strong winds and coastal impacts, with the most devastating effects occurring along the south and west-facing shores. Large waves and storm surge swept away cars, homes, and roads in the Poʻipū area, with one fatality at Nomilo Fishpond. Another wind-related fatality occurred on Oʻahu.

Heavy rainfall and flooding associated with Lowell were also significant on Kauaʻi, where 12 to 22 inches of rain fell on the 7th and 8th. Several sections of Kūhiō Highway were closed in the Hanalei and Wainiha areas because of significant rises in the Hanalei and Wainiha Rivers, as well as a flash flood fatality in the Wainiha area. Additional rain bands and terrain-enhanced showers brought 2 to 6 inches of rain to southeast-facing slopes and higher elevations of the remaining islands.

As Lowell weakened and moved northwest of the state, winds decreased to light and variable overnight into September 9 and rainfall diminished over the western islands. However, lingering moisture continued to produce showers over southeast Maui County and the Big Island. Rainfall rates were generally on the lower end, but the 1 to 2 inches of rain on the afternoon of the 9th was enough to cause flooding between Nā’ālehu and Pāhala, closing portions of Highway 11 in both directions. Ground saturation and elevated streamflow from rainfall over the previous several days likely contributed to the flooding. An additional 1 to 4 inches fell across eastern and southern portions of the Big Island through the morning of September 10. More typical trade wind conditions returned through the middle of the month, with light to moderate easterly trades and drier, more stable air through the 14th. Shower activity became more isolated and favored windward areas. 

Trade winds then increased to moderate and breezy levels as moisture associated with the remnants of Tropical Storm Norbert moved in from the east. The resulting wet trade wind pattern continued through the 18th, with deep tropical moisture and modest instability producing periods of heavy rain over windward and mauka areas. Most of the rainfall occurred between the 16th and 17th, with totals of 2 to 5 inches, though no significant flooding was observed. 

After a brief period of drier conditions and scattered windward showers through the 22nd, another significant tropical weather event developed late in the month as Tropical Depression 15-E strengthened into Hurricane Nolo south of the Big Island. Trade winds became very strong and gusty while windward showers increased from east to west through September 25 as Nolo stalled about 150 miles south of South Point. The storm then made an abrupt turn to the west on the 26th, passing well south of the island chain. Nolo produced some of the heaviest rainfall of the month for Maui and the Big Island. Windward Maui received 3 to 8 inches over two days, while northern through southeastern portions of the Big Island received 8 to 15 inches. Rainfall rates on the Big Island were generally modest, but the prolonged rainfall resulted in flooding and road closures in the Kaʻū and Puna Districts between Waiʻōhinu and Nīnole, particularly along and near Highway 11. 

Drier and more stable conditions returned on the 27th, with trade winds shifting out of the southeast and south over the next few days as Hurricane Nolo moved northward then stalled a few hundred miles west of Niʻihau. Wind speeds gradually decreased during this time for all but Kauaʻi and Niʻihau, where winds increased as Nolo made its closest approach. Nolo began a slow turn back westward on the 29th, drawing up deep tropical moisture along the east side of the storm and increasing showers over Oʻahu and areas westward through the end of the month. 24-hour rainfall totals on most of Kauaʻi and Oʻahu were a relatively modest 1 to 3 inches. However, higher amounts of 4 to 6 inches on the higher slopes of Kauaʻi, including nearly 16 inches at Mt. Waiʻaleʻale, were enough to drain down the north slopes and cause flooding over Kūhiō Highway at the Hanalei River Bridge, closing the road in both directions. Bookended by significant impacts from two tropical weather systems, September closed out a very wet dry season for Hawaiʻi. 

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

Impressive rainfall amounts from the close passages of Hurricanes Lowell and Nolo resulted in all reporting stations coming in well above average for the month, including several with totals 4 to 8 times their usual September amounts. The USGS gage on Mt. Waiʻaleʻale had the highest monthly total for the island and the state with 68.68 inches (227% of average), which was the wettest September in its period of record (since 2003). This site also had highest daily total for the island and the state with 15.79 inches on the 30th. Eleven sites on the island had their wettest September in over a decade or in their respective periods of record: Hanalei Ua Net (record, since 1991, missing data in 2010); Hanapepe Ua Net (record, since 1993); Kilohana USGS (since 2010, missing data in 2023); Mōhihi Crossing USGS (Period of Record [POR] since 2008); Mana RAWS (since 2012); Puʻu Opae RAWS (POR since 2010); Waimea Heights RAWS (POR since 2010); Waiakoali USGS (POR since 2011); Waialae RG USGS (POR since 2010); Mt. Waiʻaleʻale USGS (POR since 2003); Wailua Exp Station Ua Net (record, since 1991).

The year to date (YTD) totals and percentages of average were above average at all stations this month as well. The highest YTD total for the county and the state is at Mt. Waiʻaleʻale with 404.53 inches (138% avg), which is nearly 100 inches higher than the next highest YTD total in the state (313.87 inches at Puʻu Kukui on Maui).

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

The majority of sites had above average rainfall for September, with several over 200%. However, due to the dominant wind flow for the month being northeast to east, the leeward areas didn’t get as much rain and came in around 80 to 90% of average for the month. Even a couple sites on the upper leeward side of the Koʻolau Mountains came in below average due to the sharp rainfall gradient in that area. The highest total for the month occurred at the USGS’ Tunnel RG with 22.00 inches, (251% of average). The highest daily total came from the USGS’ Kamananui RG with 7.08 inches on the 6th. This site also had the wettest September in its period of record (since 2012). The Makaha Ridge RAWS had its wettest September since 2015. In addition, the Honolulu International Airport set a daily rainfall record of 0.84 inches on the 30th (old record was 0.64 inches in 1953).

The year to date (YTD) totals are all near to above average. The highest YTD total for the island came from the USGS Moanalua RG with 192.87 inches (204% of average). 

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

All but one site in the county came in above average for this month, with a few around 3 to 4 times (and one around 11 times) their typical September values. The USGS’ W. Wailuaiki Stream gage had the highest monthly total in the county with 43.11 inches (304% of average), as well as the highest daily total of 8.25 inches on the 6th. This site also recorded the wettest September in its period of record (since 2003), with the caveat of missing data from 2012 through 2015. The Kahului Airport set a two daily record daily rainfall records: 0.16 inches on the 6th (old record was 0.12 inches set in 2018) and 0.12 inches on the 8th (old record was 0.09 inches set in 1987). 

The year to date (YTD) totals for all reporting sites in the county were still between 100 and 400% of average. The highest YTD total remains at Puʻu Kukui with 313.87 inches (112% of average). 

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

All but one site on the island came in well above average for August. With most of the rain falling across the north through southeast portions of the island, these areas ended up with a rather impressive 500 to 1300% of their usual August values. In addition, nine sites (out of those included in this summary) recorded daily rainfall amounts of 20 inches or more on the 15th, including the highest amount on the island and statewide of 30.50 inches at the Nene Cabin RAWS. The USGS’ site at Kawainui Stream had the highest monthly total for the island again this month with 41.24 inches (462% of average). The Hilo Airport set a record daily rainfall record on the 15th with an amount of 6.82 inches (old record was 5.10 inches set in 1969). Several sites had their wettest August since Hurricane Lane in 2018, but came in second to those values. Thirteen sites recorded their wettest August this year: Kahua Ranch Ua Net: record-since 1992, Missing data in 2015); Kapāpala Ranch (since 1949); Kapāpala RAWS (since 2015, which beat their rainfall amount from Hurricane Lane in 2018); Kahuku Ranch RAWS (since 2016); Kamuela Upper Ua Net (record-since 1992); Kawainui Stream USGS (since 2010); Lower Kahuku RAWS (since 2015); Mauna Loa Observatory climate site (since 2005); Nene Cabin RAWS (since 2015); Puʻu Aliʻi RAWS (since 2012); Pāhala Ua Net (record-since 1991, Missing data in 2023); South Point NWS (since 2004, Missing data in 2011, 2024), and Waimea Plain SCAN (since 2012, Missing data in 2015).

All of the year to date (YTD) totals were near to above average for the island, with the exception of Puhe CS on the leeward Kohala coast at 68%. The highest YTD total was the USGS gage at Honoliʻi Stream with 219.47 inches (144% 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