August 2015 Precipitation Summary

State of Hawaii

MONTH: August 2015

PREPARED: September 11, 2015

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

State: [Text data table for rain gages]

Above average tropical cyclone activity and a persistent deep tropical airmass fueled by sea surface temperatures more than 2 degrees Celsius above average provided the conditions for above average rainfall across the state. Less than half of the days in August involved trade wind conditions, and 16 days had heavy rain events. On average, trade wind frequency during August is near 90 percent. Records for August rainfall were shattered in several locations and will be detailed in subsequent sections.

Among the numerous heavy rain events, the most significant was caused by a large mesoscale convective system (MCS) that moved over the state from the northwest on August 23 and 24. Significant flooding impacts occurred on Oahu from widespread 2 to 5 inches of rain, including the closure of Kamehameha Highway at Waikane Stream, Kapaa Quarry Road, and several locations on the H-1 freeway. Heavy rainfall hit the Hana area hard as more than 6 inches of rain closed Ulaino Road and the Hana Highway near Kipahulu. Piilani Highway was also closed on the south side of Haleakala due to the flooding of a low water crossing at Hawelewele Gulch near mile marker 29. Several public parks, including Wainapanapa State Park and the popular Iao Valley State Park, were also closed due to the heavy rains. On the Big Island, heavy rainfall hit the Puna District and closed Pohaku Drive at the Waipahoehoe Stream low water crossing, and the intersection of C Road and Ninth Road in Hawaiian Acres.

Prior to the big MCS event, a surface trough that was a former tropical disturbance helped trigger intense afternoon thunderstorms over the Hamakua and Kohala slopes of the Big Island on August 17. Flash flooding closed roads near Kawaihae, Ahualoa, and Kalopa State Park, and inundated the lower portion of an apartment complex in Kawaihae. In Waipio Valley, 14 hikers were stranded by flooded streams and were rescued by fire department personnel.

Island of Kauai : [August 2015 map] [year-to-date map]

Most of the rain gages across Kauai recorded monthly totals in the above average range. The highest monthly total of 39.84 inches (114 percent of average) was from the U.S. Geological Survey’s (USGS) Mount Waialeale gage while the highest daily total of 5.16 inches came from the Kapahi gage on August 24. The wet conditions broke August rainfall records at Lihue Airport, Kokee, Hanapepe, and Anahola. In addition, Wainiha and Mount Waialeale had their highest August totals since 1991 and 2006, respectively.

Most of the rain gages across Kauai recorded monthly totals in the above average range. The highest monthly total of 39.84 inches (114 percent of average) was from the U.S. Geological Survey’s (USGS) Mount Waialeale gage while the highest daily total of 5.16 inches came from the Kapahi gage on August 24. The wet conditions broke August rainfall records at Lihue Airport, Kokee, Hanapepe, and Anahola. In addition, Wainiha and Mount Waialeale had their highest August totals since 1991 and 2006, respectively.

Due to the wet conditions in August, most of the rainfall totals for 2015 through the end of August moved into the near to above average range. Mount Waialeale had the highest year-to-date total of 198.48 inches (76 percent of average).

Island of Oahu: [August 2015 map][year-to-date map]

Most of the August rainfall totals from Oahu were in the above average range. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 27.56 inches (144 percent of average). The highest daily total, 6.02 inches on August 24, was from the St. Stephen’s Seminary gage. Honolulu Airport’s monthly total of 7.63 inches was an incredible 1363 percent of average and more than doubled the previous August record of 3.74 inches set in 2004. Records for the wettest August were also broken at Ahuimanu Loop, Aloha Tower, Hawaii Kai Golf Course, Kamehame, Kunia, Lualualei, Luluku, Maunawili, Mililani, Moanalua Stream, Niu Valley, Nuuanu, Palolo Fire Station, Poamoho, Punaluu Pump, Waihee Pump, Waimanalo, and Waipio. While not a new record, the 17.99 inches measured at the Manoa Lyon Arboretum gage was its highest August total since 1982.

Following the wet August conditions, most of the rainfall totals for 2015 through the end of August have moved into the near to above average range. The Oahu Forest NWR gage had the highest year-to-date total of 127.89 inches (89 percent of average).

Maui County: [Maui August 2015 map] [year-to-date map] [Molokai/Lanai August 2015 map] [year-to-date map]

All of the rain gages in Maui County recorded above average rainfall for the month of August. The highest available monthly total of 12.59 inches (250 percent of average) was from the National Park Service’s Puu Alii gage. The USGS’ Puu Kukui gage was restored to service in late August after a lengthy outage. While a monthly total from this site was not available, a full data record should be available from September. Kahakuloa had the highest daily total of 5.75 inches on August 19.  Records for the wettest August were broken at Kahului Airport, Molokai Airport, Kahakuloa, Kula Branch Station, Lahainaluna, Mahinahina, and Pukalani. Ulupalakua Ranch had its highest August total since 1965.

Rainfall totals for 2015 through the end of August were in the near to above average range at most of the sites in Maui County. The highest available year-to-date total was from the Puu Alii gage on Molokai. This gage has recorded 126.60 inches (182 percent of average) so far in 2015.

Island of Hawaii: [August 2015 map] [year-to-date map]

Most of the gages on the Big Island reported above average rainfall totals for the month of August. The USGS’ gage at the Saddle Road Quarry had the highest monthly total of 29.06 inches (234 percent of average) and the Pahala gage had the highest daily total of 5.20 inches on August 27. Records for the wettest August were broken at the Honaunau, Kamuela, Mountain View, and Upolu Airport gages. Hilo Airport’s 17.20 inches marked the highest August total at this location since 1991.

Rainfall totals for 2015 through the end of August shifted into the near to above average range at most of the gages across the Big Island. The USGS’ rain gage at Kawainui Stream had the highest year-to-date total of 143.37 inches (143 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