National Weather Service United States Department of Commerce

Monthly Precipitation Summary

State of Hawaii

Month: March 2018

Prepared: April 4, 2018

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

State: [Text data table for rain gages]

After a very wet February, the month of March started with fresh to strong trade winds followed by the passage of a weak cold front on March 5. The front did not produce significant rainfall, but it did pull in a cool and stable air mass within moderate to fresh northeasterly low level winds that persisted until March 13.

The second half of the month featured a shift to a wetter weather pattern across the main Hawaiian Islands with several low pressure systems and upper level disturbances moving over the state from the west. These systems produced several heavy rain events, especially over the west half of the state. The first and arguably most significant of these occurred on March 14 and 15 as a low pressure system west of the island chain destabilized the local air mass and shifted the low level winds from east-northeasterly trades to east-southeasterlies. Heavy rainfall on Kauai produced flash flooding in Hanalei River during two episodes, both of which forced the closure of Kuhio Highway for several hours near the Hanalei Bridge. Landslides near Lumahai also impacted Kuhio Highway on multiple occasions. On Maui, over 12 hours of rain along the eastern slope of Haleakala produced very localized but significant flooding from Honomaele near Hana Airport to Kipahulu. Several roads, including Uakea Road, Hana Highway at Mill Street, Haneoo Road, Waikoloa Road, and Ulaino Road were closed for several hours. The Hana Airport rain gage recorded over 6 inches in 24-hours but radar estimates were over 10 inches just upslope from Hana town and Hamoa.

Trade winds returned with more stable conditions on March 17 at mostly moderate to fresh intensities. The trades lasted until March 22 and did not return for the rest of the month. A series of fast moving disturbances coupled with a very moist low level environment produced episodes of heavy rainfall and even some severe thunderstorms from March 23 through March 31. The most notable rain event during this period occurred during the late night hours of March 23 and continued into March 24. Heavy rainfall with totals in the range of 3 to 7 inches along the slopes of Oahu’s Koolau Range produced flash flooding which closed Kamehameha Highway at Waikane Stream. Areas of heavy rainfall also affected Maui County and the Big Island but did not produce significant flooding problems. Another disturbance triggered severe thunderstorms on March 25 with one storm cell producing a tornadic waterspout just offshore from Kaneohe. Later that day, around 1 to 2 inches of rainfall occurred over the Puna District of the Big Island and near Hana on Maui but neither case produced reports of significant damage. Severe thunderstorms developed once again on March 26, this time over the South Hilo and Puna Districts of the Big Island. In addition to periods of heavy rainfall, strong localized winds from these thunderstorms tore off roofs from a couple of homes and damaged signs in Hilo. Reports of small hail and downed trees and power lines also came in from both districts, and a lightning strike started a small fire at the Hilo Medical Center.

The month ended with yet another disturbance moving over the state. This time the effects were mainly over Oahu when thunderstorms formed during midday on March 31. Intense rainfall with rates of about 4 inches per hour produced flooding which damaged some homes off of Fort Weaver Road in Ewa Beach due to a clogged drainage channel.

Island of Kauai : [March 2018 map] [year-to-date map]

While not as wet as February, most of the monthly totals for March on Kauai were in the near to above average range. The U.S. Geological Survey’s (USGS) gage on Mount Waialeale had the highest monthly total of 65.83 inches (174 percent of average) and the highest daily total of 15.36 inches on March 14. The 2-day total for March 13 and 14 was 21.76 inches. This 2-day total at Mount Waialeale was more than Lihue Airport’s rainfall total for all of 2016 (13.39 inches) and nearly as much as the 2017 total (23.55 inches). Monthly totals from the Mount Waialeale and Omao gages were the highest March totals since 2006.

All of the gages on Kauai had rainfall totals for 2018 through the end of March in the near to above average range. Mount Waialeale had the highest year-to-date total of 142.78 inches (164 percent of average).

Island of Oahu: [March 2018 map] [year-to-date map]

Most of the March monthly rainfall totals on Oahu were in the near to above average range. The USGS’ Poamoho Rain Gage No. 1 had the highest monthly total of 32.80 inches (155 percent of average) and the highest daily total of 6.68 inches on March 23. A cluster of gages along the northern half of the Koolau Range had below average totals. There were no long term March rainfall records broken on Oahu. Most locations had higher March totals in 2012 and 2014.

Rainfall totals for 2018 through the end of March were in the near to above average range at most of the gages on Oahu. There were a few gages along the leeward slopes of the Waianae Range that had near to below average totals due to lingering deficits from a very dry January. The Poamoho Rain Gage No. 1 had the highest year-to-date total of 76.99 inches (140 percent of average).

Maui County: [Maui March 2018 map] [year-to-date map] [Molokai/Lanai March 2018 map] [year-to-date map]

March totals from most of the gages across Maui County were in the near to below average range.  The USGS’ West Wailuaiki gage had the highest monthly total of 24.51 inches (85 percent of average). The highest daily total of 6.10 inches was recorded at Hana Airport during the March 14 flash flood event. Hana Airport’s 13.18 inches marked the highest March total at this location since 2005.

Most of the gages across Maui County had rainfall totals for 2018 through the end of March in the near to above average range. The West Wailuaiki gage has leap-frogged Puu Kukui and now has the highest year-to-date rainfall total in Maui County with 56.67 inches (89 percent of average). Puu Kukui’s 49.30 inches was only 51 percent of average.

Island of Hawaii: [March 2018 map] [year-to-date map]

Big Island gages posted a wide range of conditions but most of the monthly totals were in the near average range. The highest monthly total of 29.26 inches (186 percent of average) came from the USGS’ Saddle Road Quarry gage. The highest daily total was 4.65 inches on March 14 from the Papaikou Well gage.

Hilo Airport had 10.93 inches, or 81 percent of the March average. There were 24 days with measurable rainfall (greater than 0.01 inches), which was above the March average of 21 days, and there were 3 days with more than 1 inch. The last time Hilo Airport had a wet March, in 2014, there were also 24 days with measurable rain but there were 6 days with more than 1 inch which contributed to the monthly total of 18.73 inches (139 percent of average). Compared to the last couple of years, 2017 and 2016 had only 14 and 21 days of measurable rainfall, and 0 and 1 day with greater than 1 inch, respectively.

Rainfall totals for 2018 through the end of March were in the near to above average range at most of the gages in the North Hilo, South Hilo, Puna, and Kau Districts. Many of the sites in the North Kona, South Kona, and South Kohala Districts had year-to-date totals remaining in the below average range due to significant January dryness. The Saddle Road Quarry gage had the highest year-to-date total of 99.08 inches (271 percent of average).

Data Sources: Data used in this report are largely from National Weather Service sources including climate network weather observation stations at Lihue, Honolulu, Kahului, and Hilo, the Hydronet state network of automated rain gages, and selected Cooperative Observer sites.  Additional data come from automated rain gages operated by the State of Hawaii Department of Land and Natural Resources, the U.S. Geological Survey, 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.  Averages come from the National Climatic Data Center (1981-2010 series) and the Rainfall Atlas of Hawaii (http://rainfall.geography.hawaii.edu/).  Data presented here are not certified and should be used for informational purposes only.

Kevin R. Kodama
Senior Service Hydrologist
NOAA/NWS Weather Forecast Office Honolulu