August 2016 Precipitation Summary

State of Hawaii

MONTH: August 2016

PREPARED: September 8, 2016

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

State: [Text data table for rain gages]

While there were no direct hits by tropical cyclones, remnants of former tropical cyclones and a close pass by Hurricane Madeline brought abundant rainfall to many areas of the state.  On days between the tropical weather systems, the trade winds, blowing mainly at moderate to fresh intensities, produced numerous showers along the windward slopes to further boost rainfall totals for the month.

The first of the tropical systems to affect the state was the remnants of former Hurricane Frank which passed near the island chain on August 3 and 4. Enhanced showers over the windward slopes resulted in daily totals in the range of 1 to 2 inches for a few spots but no reported flooding problems. Remnants of former Tropical Storm Howard moved across the main Hawaiian Islands on August 7 and dropped another 1 to 2 inches over portions of Kauai, Oahu, and Maui, with minor flooding on northwestern Oahu and northern sections of Maui.

Arguably the most significant rainfall event of the month was not related to an active or former tropical cyclone but involved a weak tropical disturbance which passed just south of the state on August 22 through 24. The disturbance was accompanied by a deep tropical airmass with very moist and unstable conditions primed for heavy rainfall production. Several gages reported daily totals in the range of 2 to 5 inches with minor flooding occurring in portions of all four counties. Intense rainfall over the windward slopes of Oahu on the night of August 23 prompted the issuance of a flash flood warning but luckily no major roads were closed and there were no reports of significant damage.

Lastly, the month ended in dramatic fashion with the passage of Hurricane Madeline to the southeast of the Big Island. The hurricane was close enough to have its outer rain bands sweep over the Big Island’s eastern districts on August 31. The highest event rainfall totals ranged from 5 to 11 inches but were spread out over a long period which mitigated serious flooding impacts. A few low-lying, flood-prone roads in Hilo were inundated briefly but no significant damages were reported.

Island of Kauai : [August 2016 map] [year-to-date map]

Near to above average rainfall totals for the month of August occurred at most of the gages across Kauai. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 55.19 inches (159 percent of average). This was the highest August total at this site since 1991 and included 18 days with greater than an inch of rainfall. Mount Waialeale also had the highest daily total of 5.04 inches on August 2. Interestingly, a small section of leeward Kauai near Hanapepe reported totals at less than 25 percent of average. These totals were consistent with reports of the poor condition of non-irrigated pastures in the area.

Most of the gages on Kauai had near to above average rainfall totals for 2016 through the end of August. Mount Waialeale had the highest year-to-date total of 246.93 inches (94 percent of average) and passed the West Wailuaiki gage with the highest 2016 total in the state.

Island of Oahu: [August 2016 map] [year-to-date map]

In continuing the wet summer theme on Oahu, most of the gages across the island recorded above average rainfall totals for the month of August. The Waiawa, Palisades, Kahuku, Nuuanu, and the USGS’ Poamoho No. 1 gage all broke records for the highest August rainfall total. The Manoa Lyon Arboretum gage had its wettest August since 1993. The Poamoho No. 1 rain gage had the highest monthly total of 32.02 inches (179 percent of average), while the highest daily total came from the USGS’ Moanalua Rain Gage No. 1 with 6.38 inches on August 22.

Rainfall totals for 2016 through the end of August were in the near to above average range for most of the gages on Oahu. The exceptions were mainly from sites along the leeward slopes of the Waianae Range. The USGS’ Poamoho No. 1 gage had the highest year-to-date total of 134.62 inches (92 percent of average).

Maui County: [Maui August 2016 map] [year-to-date map] [Molokai/Lanai August 2016 map] [year-to-date map]

Most of the rain gages across Maui County recorded above average rainfall totals for the month of August. The USGS’ West Wailuaiki gage had the highest monthly total of 38.29 inches (225 percent of average) and the highest daily total of 4.96 inches on August 22. The 7.46 inches logged by the Haiku gage tied the August record set in 2000, and the Hana Airport gage had its highest August total since 1995.

A majority of the gages across Maui County had rainfall totals for 2016 through the end of August in the near to above average range. The West Wailuaiki gage had the highest year-to-date total of 239.94 inches (152 percent of average) which was the second highest total in the state. Puu Kukui, normally considered to be one of the wettest spots in the state, has recorded 119.19 inches which was just 46 percent of the year-to-date average.

Island of Hawaii: [August 2016 map] [year-to-date map]

Above average rainfall totals were recorded at most of the gages on the Big Island for the month of August. The USGS’ Saddle Road Quarry gage had the highest monthly total of 34.41 inches (277 percent of average) and the highest daily total of 9.29 inches on August 31 during the passage of Hurricane Madeline. While this daily total is impressive, none of the 1-hour accumulations during this 24-hour period exceeded an inch.  Records for the highest August rainfall total were broken at the Waiakea Uka, Mountain View, and Glenwood gages, and Hilo Airport had its wettest August since 1991.

Wet summer conditions have finally overcome severe rainfall deficits from early in the year. As a result, rainfall totals for 2016 through the end of August were in the near to above average range at most of the gages on the Big Island. Locations with continuing deficits in year-to-date rainfall were mainly from the Kona and leeward Kohala areas. The USGS’ Saddle Road Quarry gage had the highest year-to-date total of 176.79 inches (187 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